Sym-Bionic Titan - Season 1 Episode 13 The Demon Within

Lance, Ilana, and Octus go deep in to the swamp to find a Mutraddi that has crash-landed in the water. They investigate the wreckage and are attack by an amphibian-like Mutraddi that, after a seemingly easy kill, is able to bite Ilana and escape. Very slowly she transforms into the creature and attacks an alligator that was also mutated. Lance and Octus discovered that if they kill the original Mutraddi she might turn back to normal. After a short battle they killed the original Mutraddi turning Ilana back to herself.