That almost went a little bit too well.
Ok Poliwag, let's not stop a good thing, just keep digging around for now, showing Monohm not to sleep on the job. Horsea, might as well keep picking on the sleeper, just Ice Beam him.
After that, Horsea should be able to finish Monohm, so Poliwag let's turn our attention to Ralts. Digging up a tree is probably ill advised so we'll just jump up there and use Body Slam; if the branches break and bring both of you down, no worries. Horsea, go in for the kill against Monohm with Ice Beam.
After that, I want Poliwag to Doubleslap Ralts while Horsea Signal Beams it. If Monohm is still alive, switch Horsea's target to him.