Turncoat Kunoichi

Sneak {2}{W}{B} (You may cast this spell for {2}{W}{B} if you also return an unblocked attacker you control to hand during the declare blockers step. It enters tapped and attacking.)
When this creature enters, choose target creature an opponent controls. Exile that creature until this creature leaves the battlefield. If this creature's sneak cost was paid, instead exile the chosen creature.

Armaggon, Future Shark

Flash
When Armaggon enters, destroy up to three target creatures.

Mighty Mutanimals

When this creature enters, create a 2/2 red Mutant creature token.
Alliance — Whenever another creature you control enters, put a +1/+1 counter on target creature you control.

Koya, Death from Above

Flying
When Koya enters, exile up to one other target creature. At the beginning of the next end step, you may pay {3}{B}. If you don't, return that card to the battlefield under its owner's control.

Sally Pride, Lioness Leader

When Sally Pride enters, create X 2/2 red Mutant creature tokens, where X is the number of nontoken creatures you control.
Whenever Sally Pride attacks, put a +1/+1 counter on each creature you control.