Rendelith

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

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

The rendelith deals double damage to objects and structures.

The rendelith makes two Stone Hammer attacks and uses Spellcasting to cast Shatter (level 6 version).

Melee or Ranged Attack Roll: +13, reach 10 ft. or range 120 ft. Hit: 21 (4d6 + 7) Bludgeoning damage. If the target is a Large or smaller creature, it has the Prone condition. If the target already has the Prone condition, it instead takes an extra 7 (2d6) Bludgeoning damage. Hit or Miss: The hammer magically returns to the rendelith's hand immediately after a ranged attack.

The rendelith casts one of the following spells, requiring no Material components and using Intelligence as the spellcasting ability (spell save DC 19):

At will: Move Earth, Passwall, Shatter (level 6 version), Wall of Stone