Astera

Boneless. The astera can move through an occupy a space as narrow as 4 inches wide without squeezing.

Protective Coating. A creature that touches the astera or hits it with a melee attack while within 5 ft. of it takes 3 (1d6) acid damage. A creature grappled by the astera takes 3 (1d6) acid damage at the start of each of its turns.

Regeneration. The astera regains 10 hit points at the start of each of its turns. If the astera takes slashing damage, this trait doesn't function at the start of the astera's next turn. The astera dies only if it starts its turn with 0 hit points and doesn't regenerate.

Water Breathing. The astera can breathe only underwater.

Multiattack. The astera makes one Bite attack and one Latch attack.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d8+2) piercing damage.

Latch. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 11 (2d8+2) slashing damage, and the target must succeed on a DC 14 Constitution saving throw or be Paralyzed for 1 minute. The target can repeat its saving throw at the end of each of its turns, ending the effect on itself on a success. The astera latches onto the target, and occupies the same space as it.

Dissolve. The astera releases a caustic, digestive slime in an attempt to dissolve a paralyzed creature whose space it occupies. The target must make a DC 14 Constitution saving throw, taking 10 (3d6) acid damage on a failure, or half as much on a success.

Split. When an astera that is Medium or larger is subjected to slashing damage, it splits into two new asteras if it has at least 10 hit points. Each new astera has hit points equal to half the original astera's, rounded down. New asteras are one size smaller than the orignal.