Marilith

The monster has Advantage on saving throws against spells and other magical effects.

If the monster dies outside the Abyss, its body dissolves into ichor, and it gains a new body instantly, reviving with all its Hit Points somewhere in the Abyss.

The monster can take one Reaction on every turn of combat.

The monster makes six Pact Blade attacks and uses Constrict.

Melee Attack: +10 to hit. reach 5 ft. Hit: 1d10 + 5 slashing plus 2d6 necrotic damage.

Strength Save: DC 17. target: creature. Failure: 2d10 bludgeoning damage.

The monster teleports up to feet to an unoccupied space it can see.

Trigger: The monster is. Response: The monster adds to its AC against that attack, possibly causing it to miss.