Season 4, Episode 48 - "The Kecleon Caper"
17 August, 2002
On the way to Olivine City, a blimp lands in the town that Ash and friends are in. It turns out that there are two sick Pokémon on board and Brock is allowed to treat them. The two pokémon are Kecleon, and some after being healed they go on a hiding spree.
