The thing is, I'm a voter and all the ideas thrown out here fit my definition of monster. Not only would I readily vote for them, but I'd probably be a lot more likely to vote for a creative take on the prompt than for something that's more literal. Zombies are good; inner demons casting shadows on the walls of Vriska's hive or Eridan twisting himself to fit the heritage of Dualscar are "wow, what a good take!"