Bru

Amorphous. Bru can move through a space as narrow as 1 inch wide without squeezing.

Corrosive Form. A creature that touches Bru or hits it with a melee attack while within 5 feet of it takes 4 (1d8) acid damage. Any nonmagical weapon made of metal or wood that hits the pudding corrodes. After dealing damage, the weapon takes a permanent and cumulative −1 penalty to damage rolls. If its penalty drops to −5, the weapon is destroyed.

Nonmagical ammunition made of metal or wood that hits Bru is destroyed after dealing damage.

Bru can eat through 2-inch-thick, nonmagical wood or metal in 1 round(he is just a hungry lad).

Spider Climb. Bru can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Just a hug. Bru takes up its entire space. Other creatures can enter the space, but a creature that does so is subjected to Bru's Engulf and has disadvantage on the saving throw.

Creatures inside Bru can be seen but have total cover.

A creature within 5 feet of Bru can take an action to pull a creature or object out of the cube. Doing so requires a successful DC 15 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.

Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) bludgeoning damage plus 18 (4d8) acid damage. In addition, nonmagical armor worn by the target is partly dissolved and takes a permanent and cumulative −1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10.

Engulf. Bru moves up to its speed. While doing so, it can enter Large or smaller creatures' spaces. Whenever the cube enters a creature's space, the creature must make a DC 15 Dexterity saving throw.

On a successful save, the creature can choose to be pushed 5 feet back or to the side of the cube. A creature that chooses not to be pushed suffers the consequences of a failed saving throw.

On a failed save, Bru hugs the creature's space, and the creature takes 10 (3d6) acid damage and is engulfed. The engulfed creature can't breathe, is restrained, and takes 21 (6d6) acid damage at the start of each of Bru's turns. When Bru moves, the engulfed creature moves with it.

An engulfed creature can try to escape by taking an action to make a DC 15 Strength check. On a success, the creature escapes and enters a space of its choice within 5 feet of Bru(but he will be sad about it).

Split. When Bru is subjected to lightning or slashing damage, it splits into two new Brus if it has at least 10 hit points. Each new Bru has hit points equal to half the original Bru's, rounded down. New Brus are one size smaller than the original Bru.