He is a good switch-in. My thought process:
Most will start with Skarmory because it is a conservative pick. Pick a counter, effective or neutral, to Skarmory.
As soon as they fire a second Sky Attack, absorb it if you can, switch out to Chan and fire a quick thunderpunch. You will have a TP ready before they Sky Attack. Either they'll shield/swap and save what little health is left on the Skarm, or let the Skarm die.
Afterwards keep punching and depending on the switch fire off another thunder/fire/ice punch for hopefully very nice damage.
Swap into the opener Pokemon you had and hopefully you have another charge move to fire off in succession or bring out the fresher last mon.

Good luck if participating!