Kecleon

Kecleon is a stupid dumb chameleon Pokemon of the Normal type. Only in Ruby and Sapphire, it can be found on Routes 118-121 and 123, but some are invisible and require the infamous Devon Scope. The one blocking the gym in Fortree City flees, but the other Kecleons attack you. They are most frequently invisible on Route 120, where you catch Absol.

Kecleon's ability is Color Change, which can change its type depending on the attack it's hit by.

Kecleon has appeared in the anime. In fact, there were two of them.