If Portcullis is in play on my side and there are two creatures on the battlefield and my opponent brings in a creature with an ETB effect, do the ETB triggers of Portcullis and the creature that was brought in have to resolve before (1) one of the existing creatures can use an activated ability or (2) the newly brought in creature can use it's own non-tap ability?
No. When that creature enters the battlefield, both its own ETB trigger and Portcullis's ETB trigger will go on the stack. Then each player receives priority in Active Player Nonactive player order, allowing each player to cast spells and activate abilities.
If Portcullis is in play on my side and there are two creatures on the battlefield total, both on my side, and my opponent plays Fleshbag Marauder and I respond by flashing in a creature, I could sacrifice the creature I brought in, my opponent would have to sacrifice Fleshbag Marauder, and the board would return to it's original position, with Portcullis triggering but not "doing anything" as there would only be two creatures when it resolved, is that correct?
If Portcullis is in play on my side and there are two creatures on the battlefield total, both on my side, and my opponent plays Fleshbag Marauder and I respond by flashing in a creature, I could sacrifice the creature I brought in, my opponent would have to sacrifice Fleshbag Marauder, and the board would return to it's original position, with Portcullis triggering but not "doing anything" as there would only be two creatures when it resolved, is that correct?
No. You also have to take Portcullis's own triggers into account.
First, Fleshbag Marauder will ETB, causing its own trigger and that of portcullis to trigger. If you control the artifact, as in your first example, then the abilities will end up on the stack in Active Player Nonactive Player order, so the marauder's ability will go on the stack first and resolve second, while portcullis's trigger will go on the stack second and resolve first, as per last-in-first-out order.
Then, if you flash in another creature, portcullis will trigger again, going on top of both of the other triggered abilities, and exile it. Then the first portcullis trigger will resolve, exiling the marauder. Finally, the marauder trigger will cause you to sacrifice one of your two creatures.
If I have Portcullis in play and there are two creatures on the battlefield and I bring in a creature with a non-ETB, non-tap ability, for example Sakura-Tribe Elder, is the creature able to activate it's ability before it is exiled under Portcullis?
If I have Portcullis in play and there are two creatures on the battlefield and I bring in a creature with a non-ETB, non-tap ability, for example Sakura-Tribe Elder, is the creature able to activate it's ability before it is exiled under Portcullis?
In general, you can activate an activated ability of a creature (such as Sakura-Tribe Elder's) in response to an enters-the-battlefield ability such as Portcullis's that triggered upon that creature entering the battlefield (unless the activated ability has the tap symbol or the untap symbol in its cost and the creature doesn't have haste) (C.R. 302.6, 702.10c, 117.7).
Yes. You can respond to any triggered ability that isn't mana ability. They do not resolve immediately but rather everyone has the chance to respond first.
No. You also have to take Portcullis's own triggers into account.
First, Fleshbag Marauder will ETB, causing its own trigger and that of portcullis to trigger. If you control the artifact, as in your first example, then the abilities will end up on the stack in Active Player Nonactive Player order, so the marauder's ability will go on the stack first and resolve second, while portcullis's trigger will go on the stack second and resolve first, as per last-in-first-out order.
Then, if you flash in another creature, portcullis will trigger again, going on top of both of the other triggered abilities, and exile it. Then the first portcullis trigger will resolve, exiling the marauder. Finally, the marauder trigger will cause you to sacrifice one of your two creatures.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)