The protagonist's thought-to-be-dead sister appears before him, but it is actually a monster's tail in disguise.
Decent process is found, she disfigures into something monstruous, but sadly she is only the tail of the actual monster, who is simply hidden beneath the leaves.
There is another character which seems to mutate into a Komodo dragon in the same episode, but we only see a couple of bits of the process (face and left claw).
https://youtu.be/ZLGRdlOWdKk?t=1058