Bring Down

Assist (Another player can pay up to {3} of this spell's cost.)
Destroy target creature with power 4 or greater.

Play of the Game

Assist (Another player can pay up to {6} of this spell's cost.)
Exile all nonland permanents.

Gideon, Battle-Forged

+2: Up to one target creature an opponent controls attacks Gideon, Battle-Forged during its controller's next turn if able.
+1: Until your next turn, target creature gains indestructible. Untap that creature.
0: Until end of turn, Gideon, Battle-Forged becomes a 4/4 Human Soldier creature with indestructible that's still a planeswalker. Prevent all damage that would be dealt to him this turn.

Kytheon, Hero of Akros

At end of combat, if Kytheon, Hero of Akros and at least two other creatures attacked this combat, exile Kytheon, then return him to the battlefield transformed under his owner's control.
{2}{W}: Kytheon gains indestructible until end of turn.

Kytheon, Hero of Akros // Gideon, Battle-Forged

Dwarven Lightsmith

Assist (Another player can pay up to {5} of this spell's cost.)
When Dwarven Lightsmith enters, creatures your team controls get +1/+1 until end of turn.

Skystreamer

Assist (Another player can pay up to {4} of this spell's cost.)
Flying
When Skystreamer enters, target player gains 4 life.