MTG Salvation

Ending Pathways
Land
T: Add 1 to your mana pool.
When Ending Pathways is put into a graveyard from anywhere, remove it from the game.

(OK, I know it's a really bad card, but it's a parody on something else I've made.)

Starstruckness 3W
Creature - Spirit Incarnation
Flying
When Starstruckness is put into a graveyard from play, remove it from the game.
As long as Starstruckness is removed from the game face up, creatures you control get +1/+1.
2/2 <- Forgot p/t

Based on the way these abilities work, you've got an unstoppable infinite loop that results in the collapse of the world a draw game.

Sarnath'd.

I like the idea of Divided Attention.

Hellish Counselor has an interesting concept, but I don't think the risk/reward factor is big enough - It probably should be 2 life each turn.

I'm not good at judging planeswalkers, so I'll let someone take over.

Prismcast
Instant
Prismcast is all colors.
Target player gains 4 life if was spent to play Prismcast.
Target player draws two cards if was spent to play Prismcast.
Target player loses 3 life if was spent to play Prismcast.
Prismcast deals 3 damage to target creature if was spent to play Prismcast.
Target player puts three 1/1 green Saproling creature tokens into play if was spent to play Prismcast.

Next:

It seems as though it would work, since they're triggered abilities. So yes, you can sacrifice it to something else.

The rules stated that if there were two creature classes, it's legal to add a race.

Starlight Pyromancer 1RW
Creature - Human Cleric Wizard
At the beginning of your upkeep, you may gain 1 life.
At the beginning of each opponent's upkeep, you may have Starlight Pyromancer deal 1 damage to target creature or player.
1/1

Next:
Choose one -
Human Elemental;
or
Human Spirit

No, Maelstrom Archangel says you don't have to pay the mana cost, and this includes the cost that the Trinisphere adds.

EDIT: Sarnath'd, by a different answer. Chances are this post is wrong.

They stay artifact, but they lose all other abilities.

Blood Moon
Urborg, Tomb of Yawgmoth

Urborg says that they are swamps in addition to their other types, so they retain everything with Urborg.

Merrowbones 1UB
Creature - Merfolk Skeleton
Islandwalk
UB: Regenerate Merrowbones.
2/2

Next: Snake Hound (Note - I had to do this once before on a different forum...)

Tiger's Eye Golem
Artifact Creature - Golem
Affinity for Mountains and for Plains
First strike
3/2

Trophy Hunter of Eyeblights!

Next:

_____ 1BB
Artifact Creature - Human Rogue
Flash
When ~ comes into play, draw a card for each card an opponent discarded this turn.
~ gets +1/+0 for each artifact card in your graveyard.
1/1
EDIT: Dream Salvage Slasher is correct. Your turn, Moss_Elemental.

The +1/+1 counters don't come back on the creature that persists. When something persists, it is treated as a new object. It comes back as a 3/2 with a -1/-1 counter on it (equivalent to a 2/1.)

EDIT: Sarnath'd twice.

Hm, this is a hard one.

Surgestream X(G/U)
Instant
Untap X target permanents. Those permanents gain shroud until end of turn.

Next: 5GWU

There are two parallel tracks next to each other that go from Barcelona to Madrid. The cities are 600 km apart.
Train 1 leaves Barcelona and heads for Madrid at 120 km/h.
At the same time, Train 2 leaves Madrid and heads for Barcelona at 80 km/h.
When the trains meet, which one is closer to Madrid?

Answer in spoiler:

PS - The white-highlight text does not work on the dark style. You could use spoiler tags, though.