A creature within 5 feet of the cube can take an action to pull a creature out. Doing so requires a successful DC 12 Strength check, and the creature making the attempt takes 3 (1d6) acid damage.
The cube can hold only one Medium creature or up to four Small or Tiny creatures inside it at a time.
Transparent. Even when the cube is in plain sight, it takes a successful DC 15 Wisdom (Perception) check to spot a cube that has neither moved nor attacked. It takes a DC 18 (Perception) check to spot a cube that is engulfing another creature. A creature that tries to enter the cube's space while unaware of the cube is surprised by the cube.
Unarmed Acid Strike. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 6 (2d6) acid damage.
Engulf. The cube moves up to its speed. While doing so, it can enter Medium or smaller creatures' spaces. Whenever the cube enters a creature's space, the creature must make a DC 12 Dexterity saving throw.
On a successful save, the creature can choose to jump 5 feet back or to the side of the cube. A creature that chooses not to jump suffers the consequences of a failed saving throw.
On a failed save, the cube enters the creature's space, and the creature takes 3 (1d6) acid damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 9 (3d6) acid damage at the start of each of the cube's turns. When the cube moves, the engulfed creature moves with it.
An engulfed creature can try to escape by taking an action to make a DC 12 Strength check. On a success, the creature escapes and enters a space of its choice within 5 feet of the cube.
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