Multiattack. Two Bite attacks and one Encage attack.

Bite. Melee Weapon Attack: +8 to hit, 10 ft., one target, 13 (2d8+4) piercing damage + 7 (2d6) necrotic.

Encage. Melee Weapon Attack: +8 to hit, 5 ft., one target, 11 (2d6+4) piercing damage. If target is a Med or smaller creature DC 16 Dex save or be caged within body of bonecage constrictor. Caged creature is restrained has cover vs. attacks and other effects outside constrictor and it takes 10 (3d6) necrotic at start of each of constrictor's turns. While caged creature can see outside constrictor but can't target those outside constrictor with attacks or spells nor can it cast spells or use features that allow it to leave constrictor's body. In addition creatures caged within constrictor can't make attack rolls vs. creatures outside constrictor. Constrictor can have up to 6 Med or smaller creatures restrained at a time. If constrictor takes 20+ damage on a single turn from any source it must make DC 16 Con save at end of that turn or all caged creatures fall prone in a space within 10 ft. of constrictor. If any of the damage is thunder constrictor has disadvantage on the save. If constrictor dies caged creature is no longer restrained by it and can escape from corpse via 10 ft. of move exiting prone.

Crush. Each creature caged by constrictor must make DC 16 Str save or take 11 (2d6+4) bludgeoning damage.