Elekid, start off this round by hitting the Mudkip with a Thunderbolt. Next, while Mudkip is trying to use Rain Dance (which won't work in this arena), hit it with a Toxic. Then, use another Thunderbolt on Mudkip.

Slowpoke, back up until you are at least five feet away from Oddish. Then, use triple Dream Eater on Oddish.