Heartless Summoning

Creature spells you cast cost {2} less to cast.
Creatures you control get -1/-1.

Cloudstone Curio

Whenever a nonartifact permanent you control enters, you may return another permanent you control that shares a permanent type with it to its owner's hand.

Corpse Knight

Whenever another creature you control enters, each opponent loses 1 life.

Endless One

Endless One enters with X +1/+1 counters on it.

Ugin's Conjurant

Ugin's Conjurant enters with X +1/+1 counters on it.
If damage would be dealt to Ugin's Conjurant while it has a +1/+1 counter on it, prevent that damage and remove that many +1/+1 counters from Ugin's Conjurant.