If the animated coffin is motionless at the start of combat, it has advantage on its initiative roll. Moreover, if a creature hasn't observed the coffin move or act, that creature must succeed on a DC 18 Intelligence (Investigation) check to discern that the coffin is animate.
Spider Climb
The animated coffin can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Actions
Multiattack
The animated coffin makes two Slam attacks.
Slam
Melee Weapon Attack+5 to hit, reach 5 ft., one target. 12 () 🔨 Bludgeoning damage.
Entrap
Melee Weapon Attack+5 to hit, reach 5 ft., one Large or smaller creature. The target has the condition (escape DC 13). Until this grapple ends, if the target is not an Undead, the target has the condition and takes 14 () 🏹 Piercing damage at the start of each of its turns. The animated coffin can grapple only one creature at a time.