Animated Chest

 Aberrant Magic. The chest has a 25 percent chance that an Astral Crawler climbs out of the chest when the chest opens. There is also a 25 percent chance that an Astral Crawler fuses with the chest, causing the chest to gain the following actions: 

• Multiattack. The chest can make one attack with its tentacles and one with its bite.           
• Tentacles. Melee Weapon Attack: +6 to hit, reach 10 ft., one creature. Hit: 18 (4d6 + 4) bludgeoning damage. The creature must make a DC 15 Intelligence saving throw, taking 33 (6d10) psychic damage, or half as much on a successful save. The target is grappled (escape DC 15) and restrained until the grapple ends. The chest can only grapple one creature with its tentacles.

A chest that gains these actions has a challenge rating of 6.                                                           

False Appearance. While the chest remains motionless, it is indistinguishable from an ordinary chest.

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

 Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage. If the target is medium or smaller, the target is swallowed by the chest, and the target is grappled (escape DC 15), and while grappled, is also restrained and blinded. A creature can use its action to make a DC 15 strength check to pull out a swallowed creature. Unless the grapple ends by the start of the chest's next turn, the target is sent to the Astral Plane.