They are based off alien plants, as the original Clone Lumpy grew out of a pod. The pod plants, which grew from a seed that fell to Earth in a meteorite, grew extremely fast in just a few seconds. It is unknown what planet it originally came from. The Pod Lumpys are extremely hard to destroy, as whenever one has a bodypart severed or gets cut in half, two Pod Lumpys grow in its place, which is a similarity to real plants, where in which they can grow a whole new plant just from a part cut off of it, or it could be similar to coppicing. Lumpy took advantage of this by cutting the Pod Lumpys up numerous times, so he could use them to do his chores and wait on him. They appear to be immune to certain poisons, but they get knocked out for a short time. The only way to kill the Lumpy Clones could be by crushing or (possibly) burning them, as one Pod Lumpy was crushed by a washing machine and another was seen running around on fire; if either method does work, the crushing may work because there is no room for the pod lumpy to regenerate its damaged areas, and the fire is simply because it's a plant, it burns like any other living thing.
Lumpy is the only character that the Lumpy Clones seem to acknowledge, as they mistake the other characters for things that Lumpy wanted cleaned (such as when one clone cleaned Sniffles' glasses, possibly mistaking his for a window) or fixed (such as when when one clone hammered in Petunia's head). One clone also crushed Cuddles with a mop while another was about to chop up Toothy like firewood, from this, it may be possible to liken the Pod Lumpys to a computer: they are very efficient learners, but they only know what they have been taught. The example being one Pod Lumpy cleaned Sniffles' glasses, thinking that it was a window, because it had not been taught that it wasn't another window. Despite killing three characters, the Pod Lumpy's aren't necessarily evil, just extremely dim-witted.
They look like Lumpy because he touched the original seed. If another character had planted the seed, the pod creatures likely would have resembled that character.