Animated Coffin

Antimagic Susceptibility. The coffin is incapacitated while in the area of an antimagic field. If targeted by dispel magic, the coffin must succeed on a Constitution saving throw against the caster's spell save DC or fall unconscious for 1 minute.

False Appearance. While the coffin remains motionless, it is indistinguishable from a normal coffin.

Death's Door. When a creature enters the coffin for the first time or starts its turn there, it must make a DC 17 Constitution saving throw, taking 6d8 necrotic damage on a failed save, or half as much on a successful one. If this damage reduces a creatures hit points to zero, it dies and is instantly reanimated as a zombie. This zombie is expelled from the coffin along with the normal skeletons created by the Belch Undead action next time the coffin uses it. 

Impower Dead. The coffin chooses one undead within 60 feet of it. The targeted undead has advantage on its next attack roll or saving throw. 

Reaching Grasp. Melee Weapon Attack: +7 to hit, reach 15 ft., 1 target. Hit: 15 (3d8 + 3) bludgeoning damage plus 5 (1d10) necrotic damage. A creature hit by this attack must succeed a DC 17 Dexterity saving throw or be dragged inside the coffin and subjected to the Death's Door trait. 

Boney Shrapnel. Ranged Weapon Attack: +5 to hit, range 20/60 ft., 1 target. Hit: 21 (4d10 + 1) piercing damage plus 5 (1d10) necrotic damage. 

Belch Undead. The coffin lets loose a torrent of bones in a line 15 feet lone and 5 feet wide. Any creature caught in this path must make a DC 17 Dexterity saving throw, taking 18 (3d12) bludgeoning damage on a failed save or half as much on a successful one. Additionally, 1d6 skeletons rise from the bones in unoccupied locations within 5 feet on the line.