EVs aren't essential for moveset advice, unless the person hasn't clarified what it is they want from the set (which Celadon has.)
Anyway, if a Modest Kecleon is what you want, here it is:
Kecleon @ Zoom Lens/Wide Lens
Modest
Colour Change
- Thunder
- Blizzard
- Fire Blast
- Nasty Plot
Requires re-breeding, and isn't really the greatest set in the world by any stretch of the imagination thanks to the moves Kecleon is forced to rely on here - Base 60 Sp.Attack is poor no matter how much EV Training you do with it, and Kecleon's Speed manages to be even worse. The item is designed to boost the accuracy of Kecleon's attacks - apparently Zoom Lens is supposed to boost your accuracy as long as you go last, although I've heard several people say it in fact doesn't boost accuracy at all, and boosts crit chance instead. If it boosts crit chance, pick the Wide Lens instead.
The set itself is relatively simple - Nasty Plot to power up, then start killing stuff. Thunder + Blizzard provide perfect coverage - again, the accuracy of both these moves sucks, but with Base 60 Sp.Attack Kecleon needs all the power it can get here. Fire Blast is a lot more reliable though with 95% accuracy along with the Wide Lens, and will likely be the attack of choice for the most part here. PP is another issue here too, although odds are Kecleon will end up being KO'd long before it runs out of PP thanks to it almost always going last.
I personally would run a set like this on Kecleon:
Kecleon @ BrightPowder
Adamant/Careful
Colour Change
- Focus Punch
- Sucker Punch
- Substitute
- Filler Move (Stealth Rock, Thunder Wave, Counter, Fake Out etc.)
Probably the most effective offensive set Kecleon will ever be able to wield. A bit of a guessing game to be had here - if you think the opponent will attack, Sucker Punch them in the face. If you think they won't attack, give them a Focus Punch instead. Substitute provides good protection for you whilst playing the guessing game, and BrightPowder can help out when it comes to protecting your Subs. The last move can literally be anything - the four moves I listed are my personal top picks for this, although the amount of moves Kecleon has available to it is immense, so choose whatever you want really.
