Sym-Bionic Titan (2010)

S1E13 The Demon Within

Lance, Ilana, and Octus venture into the depths of the swamp to investigate a Mutraddi spacecraft that has landed in the murky waters. During their exploration of the wreckage, they are ambushed by a mutant amphibian-like Mutraddi. Although they manage to defeat it, it bites Ilana before fleeing. Gradually, Ilana begins to transform into the creature, even attacking a mutated alligator. Realizing that eliminating the original Mutraddi might restore her, Lance and Octus engage in a fierce battle. Ultimately, they succeed in defeating the original Mutraddi, returning Ilana to her true self.