Shapechanger. The spawn can use its action to polymorph into a beast form that resembles a star-nosed mole (speed 20 ft., burrow 20 ft.), an octopus (5 ft., swim 30 ft.), a centipede (40 ft., climb 40 ft.), or back into its true form. Its statistics are the same in each form, except for the speed changes noted. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Born to Darkness. Magical darkness doesn't impede the spawn's darkvision.

Magic Resistance. The spawn has advantage on saving throws against spells and other magical effects.

Amphibious. The spawn can breathe air and water.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) piercing damage, and the target must make a DC 11 Constitution saving throw, taking 10 (3d6) poison damage on a failed save, or half as much damage on a successful one.

Invisibility. The spawn magically turns invisible until it attacks or until its concentration ends (as if concentrating on a spell). Any equipment the spawn wears or carries is invisible with it.