Perhaps a hot glue gun? You could drip some of that into drips and puddles then hit it with translucent yellow/green paint.
Hot glue won't stick to petroleum jelly, so you could coat a surface or an object with a similar shape to an MOTUC figure with it and drip some hot glue on it. Once it dries, you may be able to peel the hunk of glue off and paint it. You could end up with a dripping slime type of shape that you could drape over figures with little harm.