the evolved creature is interesting.
feet is weird tho. might make sense for something huge like an elephant like creature assuming it grows that big.
even though it has legs for better mobility, it lost its flexibility as it won't be able to hide in underground caves with water & sewer pipes in case of is discovery. Its pretty much fair game. this suggests that this creature has calcium based or cartilage based bones to support its increased weight.
Unless the Rub Dub creature is in a pupa stage (lack of a better word) of an earth worm which is most similar to. It doesn't really make sense to grow legs and tail of its rear appendage which is now closed off.
I'd replace the legs with suction tentacles, having this would help handle prey better. It apparently had some issues when prey is not in proper position for eating. not sure about the tail tho.
I'd rethink this evolved Rub Dub creature but then again this things a mutant, who knows what pile of brew it came from.