Kecleon (5e Creature)
From D&D Wiki
Small monstrosity, any alignment
Chameleon Skin. The kecleon has advantage on Dexterity (Stealth) checks made to hide.
Protean. As a bonus action, the kecleon can grant itself resistance to one damage type of its choice. When it uses this feature, it loses any damage resistance it has been granted from this feature.
Multiattack. The kecleon makes two slash attacks.
Slash. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) slashing damage plus 4 (1d8) damage of a type kecleon is resistant to.
Sucker Punch. In response to taking damage from a creature within 5 feet of it, the kecleon makes one slash attack against the creature that attacked it.
Kecleon are the masters of disguise, able to hide in broad daylight and not be seen. They could be anywhere, all around a group of adventurers and no one would notice. They will, however, get upset if they hide too well and no one notices them. They're kind of drama queens. While it's mostly for hiding, changing their colors could be a sign that the kecleon is happy or depressed, even showing whether its healthy or not.