Multiattack

The spawn of Hriggala makes two attacks: one with its bite and one with its tendrils.

Bite

Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 20 (3d8 + 7) piercing damage. If the target is a Large or smaller creature, it is grappled (escape DC 17). Until this grapple ends, the target is restrained, and the spawn can't bite another target.

Tendrils

Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (3d6 + 7) bludgeoning damage plus 14 (4d6) necrotic damage. If the target is a creature, it must succeed on a DC 17 Constitution saving throw or its hp maximum is reduced by an amount equal to the necrotic damage taken. This reduction lasts until the creature finishes a short or long rest. The creature dies if this effect reduces its hp maximum to 0. No physical trace of the creature remains when killed in this way.

Escape the Material

The spawn burrows at least 20 feet through natural rock and opens a portal to the plane of the undead at the end of this movement. The portal remains for 2d4 rounds. The spawn can't have more than one portal open at a time.