A.5. Neither banding nor a "bands with other" ability change whether a creature assigns combat damage at all. However, if that creature does assign combat damage, then banding and "bands with other" abilities can affect who can assign that combat damage and how it's assigned (C.R. 702.21j-k) — this is true even if the creature with banding or the "bands with other" ability can't assign combat damage at the moment.
B.5, C.5. No, that's not right. If the creature with first strike or double strike is blocking Benalish Hero, which has banding, and the blocking creature is eligible to assign combat damage, you can divide the blocking creature's combat damage as you choose among creatures it blocks (C.R. 702.21k). This is true even if Benalish Hero can't assign combat damage at the moment (whether because of first strike or double strike, or otherwise).
Here is how a similar scenario can play out:
Assume Benalish Hero, which you control, is in a band with Grizzly Bears. The band is blocked by Adorned Pouncer (which has double strike) and another 1/1 creature with no abilities. Also assume that none of those creatures was dealt damage this turn. The combat damage step begins.
Only Adorned Pouncer is eligible to assign combat damage. Since Adorned Pouncer is blocking Benalish Hero, which has banding, and Grizzly Bears, you can assign Adorned Pouncer's combat damage as you choose between Benalish Hero and Grizzly Bears. This is true even though Benalish Hero can't assign combat damage at the moment since it has neither first strike nor double strike. You assign Adorned Pouncer's combat damage to Grizzly Bears.
The combat damage assigned to Grizzly Bears is dealt.
All players pass.
The second combat damage step begins.
Adorned Pouncer, the other blocker, Benalish Hero, and Grizzly Bears are eligible to assign combat damage. Since the blockers both block Benalish Hero, which has banding, you can assign the blockers' combat damage as you choose between Benalish Hero and Grizzly Bears. You choose to assign the blockers' combat damage each to Grizzly Bears. Meanwhile, Benalish Hero assigns 1 damage to Adorned Pouncer and Grizzly Bears assigns 1 damage to the other blocker.
The combat damage assigned is dealt.
Grizzly Bears, Adorned Pouncer, and the other blocker are destroyed for having lethal damage.
EDIT: Add assumption after comment 43 was posted.
EDIT (Apr. 23): Correctness edit.
EDIT (Jul. 21): Correctness edit.
A.4) What if one of the mass blocking 1/1 creatures had firststrike in A3 and B3. Does the answer stay the same?
B.4) The answer stay similar even it had doublestrike instead. Am I right?
C.4) The answer stay similar even it had both doublestrike and deathtouch instead. Am I right?
A.4, B.4, C.4: If one or more of the creatures involved in questions A.3 or B.3 have first strike and/or double strike, then there will be two combat damage steps rather than one, and only certain creatures can assign combat damage during each such step (C.R. 702.4b, 702.7b). Namely:
Only creatures with first strike and/or double strike assign combat damage as the first combat damage step begins.
Only the other attacking and blocking creatures, as well as creatures with double strike, assign combat damage as the second combat damage step begins.
Thus, if the blocking creatures have first strike and/or double strike and the attacking creatures have neither, only the blocking creatures can assign combat damage during the first combat damage step (neither banding nor a "bands with other" ability can change this).
C.4: Deathtouch doesn't directly affect the answers given in A.3 or B.3, with the exception that it may make certain combat damage lethal that it otherwise wouldn't be (C.R. 702.2c, 704.5h).
A.3, B.3. Yes. Since the two creatures are blocking Benalish Hero, which has banding, you can divide those two creatures' combat damage as you choose among creatures blocked by those two creatures (C.R. 702.21k). Thus, you can choose, for example, that both creatures' combat damage are assigned to a single creature, regardless of the amount of combat damage that is.
C.3. Yes. The answers to A.3 and B.3 are the same if, instead of Benalish Hero, the two 1/1 creatures are blocking Ertai and another legendary creature (blue or otherwise) while you control Seafarer's Quay.
A.2) All damage distribution priorities stay normal and the Banding like abilities that modify damage distribution doesn't work both attacking and blocking as long Ertai is stays unbanded both blocking and attacking, Even I had a Seafarer's Quay in play with my Ertai. Am I right?
B.2) But that would change as soon Ertai is banded to another legendary creature blue or not blue, Because when Ertai is banded with another legendary creature I get all the tricks that a creature with Banding can do in combat like having the priority of damage assignment both blocking and attacking. Am I right?
C.2) Besides the need to be specific with a type to band another differences with "Banding" and "Bands with others" is when they are alone in combat or from being outside a band when attacking and blocking. A creature with "Bands with others" having no band in combat is basically just a generic and ordinary plain creature attacking and blocking without any tricks or special abilities that a creature with banding can. Am I right?
A.2. You are right in that if Ertai (with any "bands with other" ability) is blocking alone, nothing changes about the damage assignment of any creatures.
B.2. You are right in that once Ertai (with "bands with other legendary creatures") and a legendary creature (blue or otherwise) both block the same creature (in the scenario given in question 6), you can assign combat damage by the blocked creature (and thus, in this respect, "get all the tricks that a creature with Banding can do in combat" as a result).
C.2. You are right in that if a creature with a "bands with other" ability is attacking alone or blocking alone, that creature is treated no differently than the same creature without any "bands with other" abilities. In other words, if that creature is attacking alone or blocking alone, ignore whatever "bands with other" abilities it may have.
A.1. You are right, provided the attacking player chooses that and Ertai alone blocks the creature in question.
B.1. Yes, since then it would be you, not the active player, that would decide how the creature with trample assigns the combat damage (C.R. 702.21j).
C.1. Yes, since each of them would have "bands with other legendary creatures" and the other would be a legendary creatureassuming they are both legendary creatures and both have "bands with other legendary creatures".
The answers to B.1 and C.1 don't change if Ertai and a nonblue legendary creature, rather than Ertai and a blue legendary creature, block the same creature. (The answer to A.1 involves Ertai blocking alone rather than Ertai blocking together with another legendary creature, blue or otherwise.)
D.2. Yes. This is true whether the legendary creature that blocks the same creature Ertai does is blue or nonblue.
A. Yes. More precisely, you can assign 6 combat damage to the player or planeswalker they're attacking (1 from the 2/2 and 5 from the 5/5).
B. Yes. More precisely, you can assign at most 5 combat damage to the player or planeswalker concerned, not 6, since the 2/2 creature without trample has to assign all its combat damage to blocking creatures, not just some of it (C.R. 510.1a).
C. Yes. More precisely, you can assign at most 2 combat damage to the player or planeswalker concerned, since the 5/5 creature without trample has to assign all its combat damage to blocking creatures, not just some of it (C.R. 510.1a).
D. You are right in that you cannot assign an attacker's combat damage merely because a creature with "bands with other legendary creatures" (as opposed to banding) is blocking alone, as you could because a creature you control with banding (such as Benalish Hero) is blocking alone.
D.1. You are right that banding works differently from "bands with other" when a creature blocks.
E. You are right in that Ertai (with "bands with other legendary creatures") couldn't let you assign combat damage by creatures it blocks when Ertai blocks alone, in question 6, unlike Benalish Hero (with banding), which does let you assign combat damage by creatures it blocks when Benalish Hero blocks alone, in question 5.
F. No, you are not right. If you control Seafarer's Quay and block the same creature with Ertai (with "bands with other legendary creatures") and another legendary creature, you can assign the combat damage of the blocked creature (C.R. 702.21j). Likewise, if you control Seafarer's Quay and attack with Ertai (with "bands with other legendary creatures") and another legendary creature, and the same creature blocks both, you can assign the combat damage of the blocking creature (C.R. 702.21k).
G. Not exactly. If Ertai is blocking alone (even though it has "bands with other legendary creatures"), the attacking player still decides how the attacking creature assigns combat damage. Thus, in the scenario in question 6, that player can choose, for example, to have the 7/7 creature with trample assign 1 combat damage to Ertai and 6 combat damage to the player or planeswalker it's attacking (C.R. 702.19b, 510.1a). However, this is a choice the attacking player could make — the attacking player can choose instead to have the 7/7 creature with trample assign all 7 of its combat damage to Ertai (C.R. 702.19b, 510.1a).
It's important to remember that generally, if only one creature blocks a band, each creature in that band will thereby be blocked by exactly one creature (C.R. 702.21h). Thus, each creature will then normally "assig[n] all its combat damage to [the blocking creature]" (C.R. 501.1c). However, you "take into account [in part] damage from other creatures that's being assigned during the same combat damage step" to determine whether lethal damage is assigned to a creature (C.R. 702.19b; see also C.R. 510.1c). See also this thread.
1. You can have the 2/2 creature assign 1 combat damage to the blocking creature. Thus, because both attacking creatures are blocked by the 1/1 creature and that creature is assigned lethal damage, you can assign the excess combat damage of both creatures with trample to the player or planeswalker they're attacking.
2. You can have the 2/2 creature assign 2 combat damage to the blocking creature. Thus, because both attacking creatures are blocked by the 1/1 creature and that creature is assigned lethal damage, you can assign all the combat damage of the 5/5 creature with trample to the player or planeswalker it's attacking.
3. You can have the 5/5 creature assign 5 combat damage to the blocking creature. Thus, because both attacking creatures are blocked by the 1/1 creature and that creature is assigned lethal damage, you can assign all the combat damage of the 2/2 creature with trample to the player or planeswalker it's attacking.
4. A player can declare that either—
one or more creatures with banding and up to one creature without banding, or
one or more creatures with a given quality, at least one of which has "bands with other" for that quality,
are all in an attacking band (C.R. 702.21c).
Also, the player who assigns certain combat damage can change if a creature blocks or is blocked by—
a creature with banding, or
two or more creatures with a given quality, at least one of which has "bands with other" for that quality
(C.R. 702.21j-k).
5. Since the blocking creature (Benalish Hero) has banding, the defending player (rather than the active player) chooses how combat damage from creatures Benalish Hero blocks to Benalish Hero is assigned (C.R. 702.21j). Thus, the defending player can choose, in this scenario, to assign all 7 combat damage to Benalish Hero, since that is one legal damage assignment in this scenario (C.R. 702.19b, 510.1a).
6. In this scenario, if both Ertai and another legendary creature (not Ertai alone, but not just Ertai and another blue legendary creature) block the same attacking creature, the defending player (rather than the active player) chooses how combat damage from attacking creatures to them is assigned (C.R. 702.21j, 108.1). Thus, in this scenario—
if Ertai and another legendary creature block the same 7/7 creature with trample, the defending player can choose to assign all 7 combat damage of the creature with trample divided as they choose among Ertai and the other legendary creature (C.R. 702.19b, 510.1c, 510.1a), but
if Ertai alone blocks the 7/7 creature with trample, the active player decides how the attacking creature's combat damage is assigned as normal (C.R. 510.1).
There is no card with an effect that says to put a +1/+1 counter on something "until end of turn". Even Bounty of the Hunt doesn't do this.
However, an effect that says a creature "gets +1/+1 until end of turn" is not the same as putting a +1/+1 counter on that creature (the former is a continuous effect under C.R. 611.1, while the latter is a one-shot effect under C.R. 610.1; see also C.R. 613.3c). As a result, proliferating can't put a +1/+1 counter on that creature unless that creature already has a +1/+1 counter on it (C.R. 701.26a). In general, a counter is put on a permanent only if the effect says "put ... counter[s]", "give ... counter[s]", "move ... counter[s]" (C.R. 121.5), or "enter[s]" or "put ... onto" or "return ... to" "the battlefield ... with ... counter[s]" (C.R. 121.6). See also this thread.
EDIT (Apr. 17, 2020): Edited to conform to rule update with Ikoria: Lair of Behemoths.
Under current rules, to "proliferate means to choose any number of permanents and/or players that have a counter, then give each exactly one additional counter of a kind" already there (C.R. 701.26a). The permanents chosen this way need not all be controlled by the same player, and more than one player can be chosen this way.
What will beis new with War of the Spark is that while proliferating, if a permanent or player has counters of two or more different kinds (e.g., a phylactery counter and two +1/+1 counters), that permanent or player is given a counter of each such kind (in this example, one phylactery counter and one +1/+1 counter) rather than one counter of only one such kind (C.R. 701.26a). Proliferating still involves "choos[ing] any number of permanents and/or players that have a counter"; the permanents chosen this way need not all be controlled by the same player, and more than one player with counters can be chosen this way (C.R. 701.26a).
Proliferating doesn't let you put a -1/-1 counter on a permanent or player without any -1/-1 counters on it, or a counter of any other kind on a permanent or player without that kind of counter on it (C.R. 701.26a).
In any case, if a -1/-1 counter is put on a permanent with a +1/+1 counter on it, or vice versa, +1/+1 and -1/-1 counters are removed from that permanent in pairs as a state-based action (C.R. 704.5q). For the purposes of proliferating, +1/+1 counters and -1/-1 counters are two different "kinds" of counters (C.R. 121.1, 121.1a).
Also, the "-3" loyalty symbol means "Remove three loyalty counters from this permanent", not, say, "Put three negative loyalty counters on this permanent" (C.R. 107.7).
EDIT (May 1): Edited.
EDIT (May 3): Edited now that War of the Spark is released.
EDIT (Jun. 20): Further edited.
An effect that says to put a spell somewhere instead of into its owner's graveyard as it resolves (as found, for example, in Feather's triggered ability, buyback [C.R. 702.26a], and rebound [C.R. 702.87a]) is not a self-replacement effect (C.R. 614.15). An effect that says to exile an object "instead of putting it anywhere else any time it would leave the stack" (as found in flashback [C.R. 702.33a] and aftermath [C.R. 702.126a]) is not a self-replacement effect either (C.R. 614.15). Both kinds of effects are not an exception to the general rule that if two or more replacement effects would affect where a spell would go, the controller of that spell chooses which effect applies (C.R. 616.1, 616.1d).
Self-replacement effects are "not continuous effects" (C.R. 614.15). Examples of self-replacement effects are found in Remand, Urza's Mine, Cabal Ritual, and Snowfall (C.R. 108.1). All four of these cards use self-replacement effects to modify how earlier text in the card is to be interpreted (C.R. 614.15; see also C.R. 608.2c). (For Cabal Ritual, the self-replacement effect appears in a separate ability because of the threshold ability word, but it's still considered a spell ability [C.R. 112.3a]). See also this thread.
Generally, there are only two possible cases for Dramatic Reversal after it's cast:
Either Dramatic Reversal leaves the stack before it resolves (e.g., because it's countered), so that it won't resolve and won't untap any permanents...
Or Dramatic Reversal resolves (in which case it will be on the stack, not in the graveyard), it untaps all nonland permanents "you control", and only afterwards goes to the graveyard (C.R. 608.1, 608.2c, 608.2k).
Feather's triggered ability cares what the instant or sorcery spell targets only at the time the spell is cast (C.R. 601.2i, 603.2). The ability doesn't care what the spell targets at any other time, including when that spell or that ability would resolve (Feather's triggered ability doesn't have an intervening "if" clause, for example [C.R. 603.4; compare that ability with Ink-Treader Nephilim's]). (However, a spell with targets will fail to resolve if all of them are illegal [C.R. 608.2b].) Notably, Feather's triggered ability won't trigger if the spell didn't target a "creature you control[led]" at the time the spell was cast, but the spell then targets a "creature you control" afterwards (whether because one of that spell's targets became a "creature you control" due to awaken [C.R. 702.112a], because one of that spell's targets changed from a player to a "creature you control", or otherwise). See also this thread, this thread, and this thread.
Thus, for example, if Ondu Rising targeted a noncreature land as you cast that spell, Feather's triggered ability won't trigger for that spell, even if that land is a creature you control by the time Ondu Rising resolves (C.R. 702.112a).
Similarly, if Lightning Bolt targeted a player as you cast that spell, Feather's triggered ability won't trigger for that spell, even if Lightning Bolt's target then changes to a creature you control due to Redirect (C.R. 114.4).
EDIT (May 15): Add link to another relevant thread.
EDIT (May 16, 2019; May 21, 2020): Clarification.
Assuming you control Mountain Stronghold, Squee, and Ib Halfheart, and you're about to declare an attack:
1. You can declare that Squee and Ib Halfheart are both in a band (C.R. 702.21c).
2. If you also control Benalish Hero, you can declare that Benalish Hero and either Squee or Ib Halfheart are in the same attacking band, but you can't put all three in the same band (C.R. 702.21c).
3. You can put Squee or Ib Halfheart and any number of other legendary creatures (including Karn) in the same attacking band (C.R. 702.21c).
4. In general, you can't declare that a red legendary creature and Raging Goblin are in the same attacking band, since Raging Goblin isn't legendary (C.R. 702.21c).
5. There is no limit to the number of attacking bands you can declare, "but each creature may be a member of only one of them" (C.R. 702.21c).
For the purposes of Finale of Promise, a split card (not: "double card" or "hybrid card") in your graveyard has the combined mana costs and combined card types of its two halves (C.R. 708.4, 708.4b, 400.1), and that card's "mana value [is] determined from its combined mana cost" (C.R. 708.4b). Thus, for example, Carnival & Carnage in your graveyard is an instant sorcery card with combined mana cost 2(B/R)BR, making that card's mana value 5 (not 4 and not 1) while that card is in your graveyard (C.R. 202.3, 202.3f). As a result, if you cast Finale of Promise and choose 5 or greater for X, you can target Carnival & Carnage as the "target instant card ... [in] your graveyard ... with mana value X or less" or the "target sorcery card [in] your graveyard ... with mana value X or less" (C.R. 603.2b-c), so that you may cast either half of that card when Finale of Promise resolves (C.R. 708.3).
EDIT (Apr. 21): Edited.
EDIT (Sep. 24): Correction in quoted text.
EDIT (Jun. 10): Edited.
EDIT (May 3, 2021): Edited, including to conform to rule update with Strixhaven.
If two Chandra abilities you control of the kind you cited resolve this turn, and you didn't cast an instant or sorcery spell in between, both abilities will apply to the same "next" instant or sorcery spell you would cast this turn. Each such ability will create a delayed triggered ability that triggers separately when that same spell is cast (C.R. 603.2, 603.7). See also this thread. Note that Chandra's second ability applies only to instant and sorcery spells, not other kinds of spells.
B.5, C.5. No, that's not right. If the creature with first strike or double strike is blocking Benalish Hero, which has banding, and the blocking creature is eligible to assign combat damage, you can divide the blocking creature's combat damage as you choose among creatures it blocks (C.R. 702.21k). This is true even if Benalish Hero can't assign combat damage at the moment (whether because of first strike or double strike, or otherwise).
Here is how a similar scenario can play out:
EDIT: Add assumption after comment 43 was posted.
EDIT (Apr. 23): Correctness edit.
EDIT (Jul. 21): Correctness edit.
- Only creatures with first strike and/or double strike assign combat damage as the first combat damage step begins.
- Only the other attacking and blocking creatures, as well as creatures with double strike, assign combat damage as the second combat damage step begins.
Thus, if the blocking creatures have first strike and/or double strike and the attacking creatures have neither, only the blocking creatures can assign combat damage during the first combat damage step (neither banding nor a "bands with other" ability can change this).C.4: Deathtouch doesn't directly affect the answers given in A.3 or B.3, with the exception that it may make certain combat damage lethal that it otherwise wouldn't be (C.R. 702.2c, 704.5h).
C.3. Yes. The answers to A.3 and B.3 are the same if, instead of Benalish Hero, the two 1/1 creatures are blocking Ertai and another legendary creature (blue or otherwise) while you control Seafarer's Quay.
A.2. You are right in that if Ertai (with any "bands with other" ability) is blocking alone, nothing changes about the damage assignment of any creatures.
B.2. You are right in that once Ertai (with "bands with other legendary creatures") and a legendary creature (blue or otherwise) both block the same creature (in the scenario given in question 6), you can assign combat damage by the blocked creature (and thus, in this respect, "get all the tricks that a creature with Banding can do in combat" as a result).
C.2. You are right in that if a creature with a "bands with other" ability is attacking alone or blocking alone, that creature is treated no differently than the same creature without any "bands with other" abilities. In other words, if that creature is attacking alone or blocking alone, ignore whatever "bands with other" abilities it may have.
EDIT (Jul. 21): Correctness edit.
B.1. Yes, since then it would be you, not the active player, that would decide how the creature with trample assigns the combat damage (C.R. 702.21j).
C.1. Yes,
since each of them would have "bands with other legendary creatures" and the other would be a legendary creatureassuming they are both legendary creatures and both have "bands with other legendary creatures".The answers to B.1 and C.1 don't change if Ertai and a nonblue legendary creature, rather than Ertai and a blue legendary creature, block the same creature. (The answer to A.1 involves Ertai blocking alone rather than Ertai blocking together with another legendary creature, blue or otherwise.)
D.2. Yes. This is true whether the legendary creature that blocks the same creature Ertai does is blue or nonblue.
EDIT (Apr. 1, 2020; Apr. 25, 2020): Correctness edit.
B. Yes. More precisely, you can assign at most 5 combat damage to the player or planeswalker concerned, not 6, since the 2/2 creature without trample has to assign all its combat damage to blocking creatures, not just some of it (C.R. 510.1a).
C. Yes. More precisely, you can assign at most 2 combat damage to the player or planeswalker concerned, since the 5/5 creature without trample has to assign all its combat damage to blocking creatures, not just some of it (C.R. 510.1a).
D. You are right in that you cannot assign an attacker's combat damage merely because a creature with "bands with other legendary creatures" (as opposed to banding) is blocking alone, as you could because a creature you control with banding (such as Benalish Hero) is blocking alone.
D.1. You are right that banding works differently from "bands with other" when a creature blocks.
E. You are right in that Ertai (with "bands with other legendary creatures") couldn't let you assign combat damage by creatures it blocks when Ertai blocks alone, in question 6, unlike Benalish Hero (with banding), which does let you assign combat damage by creatures it blocks when Benalish Hero blocks alone, in question 5.
F. No, you are not right. If you control Seafarer's Quay and block the same creature with Ertai (with "bands with other legendary creatures") and another legendary creature, you can assign the combat damage of the blocked creature (C.R. 702.21j). Likewise, if you control Seafarer's Quay and attack with Ertai (with "bands with other legendary creatures") and another legendary creature, and the same creature blocks both, you can assign the combat damage of the blocking creature (C.R. 702.21k).
G. Not exactly. If Ertai is blocking alone (even though it has "bands with other legendary creatures"), the attacking player still decides how the attacking creature assigns combat damage. Thus, in the scenario in question 6, that player can choose, for example, to have the 7/7 creature with trample assign 1 combat damage to Ertai and 6 combat damage to the player or planeswalker it's attacking (C.R. 702.19b, 510.1a). However, this is a choice the attacking player could make — the attacking player can choose instead to have the 7/7 creature with trample assign all 7 of its combat damage to Ertai (C.R. 702.19b, 510.1a).
1. You can have the 2/2 creature assign 1 combat damage to the blocking creature. Thus, because both attacking creatures are blocked by the 1/1 creature and that creature is assigned lethal damage, you can assign the excess combat damage of both creatures with trample to the player or planeswalker they're attacking.
2. You can have the 2/2 creature assign 2 combat damage to the blocking creature. Thus, because both attacking creatures are blocked by the 1/1 creature and that creature is assigned lethal damage, you can assign all the combat damage of the 5/5 creature with trample to the player or planeswalker it's attacking.
3. You can have the 5/5 creature assign 5 combat damage to the blocking creature. Thus, because both attacking creatures are blocked by the 1/1 creature and that creature is assigned lethal damage, you can assign all the combat damage of the 2/2 creature with trample to the player or planeswalker it's attacking.
4. A player can declare that either—
- one or more creatures with banding and up to one creature without banding, or
- one or more creatures with a given quality, at least one of which has "bands with other" for that quality,
are all in an attacking band (C.R. 702.21c).Also, the player who assigns certain combat damage can change if a creature blocks or is blocked by—
- a creature with banding, or
- two or more creatures with a given quality, at least one of which has "bands with other" for that quality
(C.R. 702.21j-k).5. Since the blocking creature (Benalish Hero) has banding, the defending player (rather than the active player) chooses how combat damage from creatures Benalish Hero blocks to Benalish Hero is assigned (C.R. 702.21j). Thus, the defending player can choose, in this scenario, to assign all 7 combat damage to Benalish Hero, since that is one legal damage assignment in this scenario (C.R. 702.19b, 510.1a).
6. In this scenario, if both Ertai and another legendary creature (not Ertai alone, but not just Ertai and another blue legendary creature) block the same attacking creature, the defending player (rather than the active player) chooses how combat damage from attacking creatures to them is assigned (C.R. 702.21j, 108.1). Thus, in this scenario—
EDIT (May 4): Correctness edit.
EDIT (Apr. 1, 2020; Apr. 25, 2020; May 22, 2020; Apr. 2, 2021): Correctness edit.
However, an effect that says a creature "gets +1/+1 until end of turn" is not the same as putting a +1/+1 counter on that creature (the former is a continuous effect under C.R. 611.1, while the latter is a one-shot effect under C.R. 610.1; see also C.R. 613.3c). As a result, proliferating can't put a +1/+1 counter on that creature unless that creature already has a +1/+1 counter on it (C.R. 701.26a). In general, a counter is put on a permanent only if the effect says "put ... counter[s]", "give ... counter[s]", "move ... counter[s]" (C.R. 121.5), or "enter[s]" or "put ... onto" or "return ... to" "the battlefield ... with ... counter[s]" (C.R. 121.6). See also this thread.
EDIT (Apr. 17, 2020): Edited to conform to rule update with Ikoria: Lair of Behemoths.
Under current rules, to "proliferate means to choose any number of permanents and/or players that have a counter, then give each exactly one additional counter of a kind" already there (C.R. 701.26a). The permanents chosen this way need not all be controlled by the same player, and more than one player can be chosen this way.What
will beis new with War of the Spark is that while proliferating, if a permanent or player has counters of two or more different kinds (e.g., a phylactery counter and two +1/+1 counters), that permanent or player is given a counter of each such kind (in this example, one phylactery counter and one +1/+1 counter) rather than one counter of only one such kind (C.R. 701.26a). Proliferating still involves "choos[ing] any number of permanents and/or players that have a counter"; the permanents chosen this way need not all be controlled by the same player, and more than one player with counters can be chosen this way (C.R. 701.26a).Proliferating doesn't let you put a -1/-1 counter on a permanent or player without any -1/-1 counters on it, or a counter of any other kind on a permanent or player without that kind of counter on it (C.R. 701.26a).
In any case, if a -1/-1 counter is put on a permanent with a +1/+1 counter on it, or vice versa, +1/+1 and -1/-1 counters are removed from that permanent in pairs as a state-based action (C.R. 704.5q). For the purposes of proliferating, +1/+1 counters and -1/-1 counters are two different "kinds" of counters (C.R. 121.1, 121.1a).
Also, the "-3" loyalty symbol means "Remove three loyalty counters from this permanent", not, say, "Put three negative loyalty counters on this permanent" (C.R. 107.7).
EDIT (May 1): Edited.
EDIT (May 3): Edited now that War of the Spark is released.
EDIT (Jun. 20): Further edited.
Self-replacement effects are "not continuous effects" (C.R. 614.15). Examples of self-replacement effects are found in Remand, Urza's Mine, Cabal Ritual, and Snowfall (C.R. 108.1). All four of these cards use self-replacement effects to modify how earlier text in the card is to be interpreted (C.R. 614.15; see also C.R. 608.2c). (For Cabal Ritual, the self-replacement effect appears in a separate ability because of the threshold ability word, but it's still considered a spell ability [C.R. 112.3a]). See also this thread.
EDIT (May 7): Add rule citations.
Thus, for example, if Ondu Rising targeted a noncreature land as you cast that spell, Feather's triggered ability won't trigger for that spell, even if that land is a creature you control by the time Ondu Rising resolves (C.R. 702.112a).
Similarly, if Lightning Bolt targeted a player as you cast that spell, Feather's triggered ability won't trigger for that spell, even if Lightning Bolt's target then changes to a creature you control due to Redirect (C.R. 114.4).
EDIT (May 15): Add link to another relevant thread.
EDIT (May 16, 2019; May 21, 2020): Clarification.
1. You can declare that Squee and Ib Halfheart are both in a band (C.R. 702.21c).
2. If you also control Benalish Hero, you can declare that Benalish Hero and either Squee or Ib Halfheart are in the same attacking band, but you can't put all three in the same band (C.R. 702.21c).
3. You can put Squee or Ib Halfheart and any number of other legendary creatures (including Karn) in the same attacking band (C.R. 702.21c).
4. In general, you can't declare that a red legendary creature and Raging Goblin are in the same attacking band, since Raging Goblin isn't legendary (C.R. 702.21c).
5. There is no limit to the number of attacking bands you can declare, "but each creature may be a member of only one of them" (C.R. 702.21c).
EDIT (Apr. 21): Edited.
EDIT (Sep. 24): Correction in quoted text.
EDIT (Jun. 10): Edited.
EDIT (May 3, 2021): Edited, including to conform to rule update with Strixhaven.