Not sure if its a concept worth taking all the way, but I'm thinking an abomination would be kind of fun. The basic idea is that its a colony of maggots using the dead it feeds on as a frame for a body. The slime it secretes would harden into a pliable, rubbery substance, so you'd get a shiny translucent gray skin with writhing, white larvae just visible beneath.
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Real sketches to come.