Spirit

The spirit can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Melee Spell Attack: +4 to hit, reach 5 ft., one creature. Hit: 4 (1d4 + 2) necrotic damage and the target's hit point maximum is reduced by an amount equal to the necrotic damage taken.. This reduction lasts until the creature finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.