Bonewall

Heavy Monster. The Bonewall is immobile and immovable

Illumination. The Bonewall sheds dim light in a 5-foot radius.

Body Split. When the Bonewall reaches 1/4 of it's maximum health, it breaks down, creating a Crumbling Skeleton from it's body.

Grafted Spellcasting. The Bonewall is a 2nd-level spellcaster. Its spellcasting ability is Strength (spell save DC 10, +4 to hit with spell attacks). The Bonewall has following Warlock spells prepared:

Cantrips (at will): chill touch                                                                                                          
2nd level (2 slots): ray of enfeeblement

Expand. The Bonewall's body expands, many arms reaching outward to grab a creature within a 10 foot radius of the Bonemass. Targeted creatures in range must make a DC 10 Dexterity saving throw. If failed, you must make a DC 15 Strength saving throw to break free.

Swipe. Melee Weapon Attack: +3 to hit, reach 15 ft., 1 target. Hit: 10 (1d10) slashing damage. When the attack lands, targeted creatures must make a DC 10 Constitution saving throw. Upon failing a save, affected creatures are affected by bleeding, taking 1d4 bleed damage at the beginning of each of their turns. 

Crush. Melee Weapon Attack: +10 to hit, reach 5 ft., 2 target. Hit: 10 (2d4 + 2) bludgeoning damage. Targeted creatures must make a DC 8 Dexterity saving throw in order to dodge the incoming attack.

Bonewall Blade. Ranged Weapon Attack: +2 to hit, range 120 ft., one target. Hit: 10 (1d8 + 2) piercing damage.