Ice Cube

Cube. The cube takes up its entire space.

Engulf. The cube can engulf an incapacitated creature by remaining on its space for 1 minute. Any engulfed creature can't breathe, is restrained, and takes 21 (6d6) acid damage at the start of each of the cube's turns. When the cube moves, the engulfed creature moves with it. 

Creatures inside the cube can be seen but have total cover. 

A creature within 5 feet of the cube can take an action to pull a creature or object out of the cube if the outer layer of the cube is shattered. Doing so requires a successful DC 17 Strength check, and the creature making the attempt takes 10 (3d6) acid damage.

The cube can hold only one Large creature or up to four Medium or smaller creatures inside it at a time.

False Appearance. While the cube remains motionless, it is indistinguishable from a chunk of ice.

Slippery. At the start of each of its turns, the cube involuntarily moves the same direction and distance it voluntarily moved last turn.

At the start of each of its turns, the cube slides down slopes at a rate of 40 feet per round. This counts as voluntary movement for the purposes of determining its movement next round.

Ram. The cube chooses one of its sides and rams into all creatures adjacent to that side. Each of these creatures takes 3 (1d6) bludgeoning damage for every 5 feet the cube has moved in the direction of the chosen side this turn, and must make a DC 17 Strength saving throw if they are huge or smaller, being pushed half the distance moved in the direction of the chosen side away from the cube and being knocked prone on a failure.

Shatter. When the cube takes bludgeoning damage, its outer layer shatters, dealing 7 (2d6) piercing damage, 3 (1d6) acid damage, and 3 (1d6) cold damage to each creature within 10 feet of the cube and reducing its armor class by 4 until the outer layer reforms, which happens at the end of the cube's next turn.