Ooze Cube. The cube fills its entire space and is semi transparent. Other creatures can enter that space, but a creature that does so is subjected to the cube’s Engulf and has Disadvantage on the saving throw, it also takes a D6 acid damage.

Creatures inside the cube have Total Cover, and the cube can hold one Large creature or up to four Medium or Small creatures inside itself at a time.

As an action, a creature within 5 feet of the cube can pull a creature or an object out of the cube by succeeding on a DC 12 Strength (Athletics) check, and the puller takes 10 (3d6) Acid damage.

Transparent. Even when the cube is in plain sight, a creature must succeed on a DC 10 Wisdom (Perception) check to notice the cube if the creature hasn’t witnessed the cube move or otherwise act.

Pseudopod. Melee Attack Roll: +4, reach 5 ft. Hit: 12 (3d6 + 2) Acid damage.

Engulf. when a creature is in the cube it does a strength saving throw to escape but has disadvantage as in the cube is like trying to move in jelly. They can not have disadvantage if a player on the outside of the cube is helping, in which case, the outside player must also make a DC12 strength saving throw. at the end of a creature's turn in the cube it must take a D6 of acid damage. 

Spew: the cube can launch a spray of acid and green slime at 1 creature within 10 feet of it.