Amorphous. The oblex can move through a space as narrow as 1 inch wide without squeezing.
Aversion to Fire. If the oblex takes fire damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.
Unusual Nature. The oblex doesn't require sleep.
Pseudopod. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit:5 (1d4 + 3) bludgeoning damage plus 2 (1d4) psychic damage.
Mind flayers unleash all manner of foul experiments upon the planes with little thought for the consequences. Here, though, I suspect another influence: Juiblex.