Bubble

Soapy Aura. An enemy that starts its turn within 5 feet of Bubble must succeed on a DC 15 Constitution saving throw or be poisoned until the start of its next turn. An enemy that touches Bubble or hits it with a melee attack takes 3 (1d6) acid damage.

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

Legendary Resistance (2/Day). If Bubble fails a saving throw, they can choose to succeed instead.

Unusual Nature. Bubble doesn’t require air, food, drink, or sleep.

Multiattack. Bubble makes two Slam attacks.

Slam. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage plus 11 (2d10) acid damage.

Soapy Suds. Bubble excretes a frothy foam replicating the grease spell.

Split. When Bubble is subjected to slashing damage, it splits into two if it has at least 10 hit points. Each new Bubble has hit points equal to half the original Bubbles, rounded down and they now have a tiny size. Once tiny they can't be split again. 

Bubble can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Bubble regains spent legendary actions at the start of their turn.

Slam. Bubble attacks once with their Slam.

Pop. Bubble pops, teleporting to an unoccupied space they can see within 30 feet of them.

Soapy Suds (Costs 2 Actions). Bubble uses Soapy Suds.