Aberrant Blob

Pack Tactics. The blob has advantage on an attack roll against a creature if at least one of the blob's allies is within 5 feet of the creature and the ally isn't incapacitated.

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

Corrosive Form. A creature that touches the blob or hits it with a melee attack while within 5 feet of it takes 2 acid damage.

Pseudopod. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) bludgeoning damage and 1 acid damage. 

Split. When a blob is subjected to lightning or slashing damage, it splits into two new blobs. Each new blob has hit points equal to half the original blob's, rounded down. New blobs are one size smaller than the original blob.