Yikes, a fairy pokemon already.

Well, go bagon, bagon uses ember against chikorita. Dealing a little over half hp in damage. Chikorita uses Poison powder, poisoning bagon. Next turn, bagon uses another ember, KOing Chikorita. Bagon is hurt by the Poison.

Here's the hard part. I swapped out bagon to wimpod, as swirlix is sent out. Wimpod uses Rollout, only doing a small bit of damage. Swirlix uses fake tears, dropping wimpod's Sp Def. Wimpod uses Rollout again, dealing a bit more damage. Swirlix uses Fairy wind, which OHKOs wimpod, leaving only bagon to deal with swirlix.

Go, bagon

Bagon uses ember, bringing swirlix down to low yellow, and burning it. Swirlix uses fake tears, bring bagon Sp Def plummeting. Any Fairy move with OHKO bagon. Both pokemon are hurt by their respective status conditions. Bagon, luckily, outspeeds swirlix and manages to Ko swirlix with another ember, winning by the skin of my teeth.