The Marshans

Hailing from the planet Mars, this wasteful race of beings travels the universe in search of planets with an energy core that they can drain for their own greedy purposes. Since they have no bodies of their own, and exist in a dust-like state, they descend upon the swamps to inhabit the bodies of beings that share their nasty and icky qualities. Animals like snakes, alligators, and bats provide a bountiful haven for possession, though they have found a few humans nasty enough to succumb to their power. Once in their host body, they are only recognizable by a mysterious third eye. Their only mission is too suck the Earth's core dry of life, but they do have one major weakness; marshmallows! Any contact with a marshmallow causes the host body to shrivel and shrink to the smallest form of its inhabitant, for instance, an alligator to a harmless lizard.