Bollymong

Shapechanging. the bollymong can use its action to poly-morph into the most feared living creature of a intelligent being within sight.

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

Familiar (variant). The bollymong can enter into a contract to serve another creature as a familiar, forming a Telepathic Bond with its willing master. While the two are bonded, the master can sense what the bollymong senses as long as they are within 1 mile of each other. While the bollymong is within 10 feet of its master, the master shares the bollymong’s Magic Resistance trait. If its master violates the terms of the contract, the bollymong can end its service as a familiar, ending the Telepathic Bond

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: (1d4 + 3) piercing damage plus (3d6)poison damage. The target must make on a dc on a failed save, or half as much damage on a successful one