just gang up on everyone and ya done
however.. i ended up befriending one creature because its attack stat was too high so they woulda obliterated me, but the only friendly stat they had was level 1 sing. befriending was a safer option here
also i swear these went through a pokemon evolution
i dont know what they were initialy but they coccooned and turned into clubs and then the clubs coccooned and turned into spikey hammers
here you can see in the up left a "find a partner" task, which appears pretty much right at the start of the stage and its how you evolve. see i beat the stage but never cleared the task! should be good enough proof.