Vengeance Strike:
The ranger can use this trick as an immediate action when an enemy adjacent to him hits an ally with a melee or ranged attack. The ranger can make a single melee attack at his highest base attack bonus against the creature who attacked his ally. (Hunter Companions can take Ranger (Skirmisher) tricks. In this case "the ranger" is the chameleon.
[dice=Chameleon To Hit (Power Attack)]1d20+2[/dice]
[dice=Chameleon Damage (Power Attack)]1d6+4[/dice]