When Aethanis Conservator enters the battlefield, choose one — • Exile target creature an opponent controls until Aethanis Conservator leaves the battlefield. • Target opponent reveals their hand and you choose a noncreature, nonland card from it. Exile that card until Aethanis Conservator leaves the battlefield.
Aethanis Undying can't block. Whenever Aethanis Undying becomes blocked by a creature, put a -1/-1 counter on that creature at end of combat. You may cast Aethanis Undying from your graveyard as long as a creature an opponent controls has a -1/-1 counter on it.