Mareshiah

A monster with telepathy can communicate mentally with any creatures within the listed radius, as long as they share a language. This doesn't give any special access to their thoughts, and communicates no more information than normal speech would.

The monster can cast its at-will spells any number of times without using up spell slots.

A constant spell affects the monster without the monster needing to cast it, and its duration is unlimited. If a constant spell gets counteracted, the monster can reactivate it by spending the normal spellcasting actions the spell requires.

A signed contract carried by Mareshiah (including draped over her horns) is immune to damage from all creatures other than her. Mareshiah is immune to mental effects that would make them destroy, nullify, or alter a contract.

Mareshiah produces an infernal contract for a single living mortal. This contract can grant a wide range of abilities and effects, akin to the power of a wish ritual but fulfilled to the letter by Mareshiah. To receive any of those benefits, the mortal must willingly sign their true name to the contract. At that point, the mortal's soul is bound to Mareshiah and Hell.

While the contract is in effect, the victim can't be restored to life except by a wish ritual or similar magic. If the mortal is restored to life by those means, Mareshiah knows which mortal came to life and can locate the creature or creatures who restored the mortal to life for 1 year, gaining the effects of a pinpoint spell. Avoiding the terms of an infernal contract is difficult and often dangerous.

3d6+15 bludgeoning, DC 42 basic Fortitude

Only when grabbed by Binding Contract

The monster deals the listed amount of damage to any number of creatures Grabbed or Restrained by it. Each of those creatures can attempt a basic Fortitude save with the listed DC. A creature that fails this save falls Unconscious, and a creature that succeeds is then temporarily immune to falling unconscious from Greater Constrict for 1 minute.

Mareshiah can cast a 10th-rank innate Scrying spell at will, but only to target a creature with which they have a contract. The target automatically critically fails its save.

The wounds from Mareshiah's Strikes resist healing.

A spellcaster or item attempting to use healing magic on a creature damaged by Mareshiah's Strikes must first attempt to counteract infernal wound (DC 42). If it isn't counteracted, the healing has no effect.

The monster can instead use Grab and choose one creature it's grabbing or restraining with an appendage that has Grab to automatically extend that condition to the end of the monster's next turn.