It That Betrays

If an opponent sacrifices an Aura, you’ll choose what it enchants as you return it to the battlefield. No player can respond to the choice. Since an Aura doesn’t target anything if it isn’t cast as a spell, you can enchant a permanent with shroud this way.

If a creature with annihilator is attacking a planeswalker, and the defending player chooses to sacrifice that planeswalker, the attacking creature continues to attack. It may be blocked. If it isn’t blocked, it simply won’t deal combat damage to anything.

The second ability triggers whenever an opponent sacrifices a nontoken permanent for any reason, not just due to the annihilator ability.

When the second ability resolves, you must return the card to the battlefield, even if you don’t want to.

If the sacrificed permanent that caused the second ability to trigger somehow leaves the graveyard before the ability resolves (possibly because it was returned to the battlefield by the ability of another It That Betrays), the ability simply won’t do anything when it resolves.

Annihilator abilities trigger and resolve during the declare attackers step. The defending player chooses and sacrifices the required number of permanents before they declare blockers. Any creatures sacrificed this way won’t be able to block.