"The Demon Within" is the thirteenth episode of Sym-Bionic Titan. It debuted on February 9, 2011.
Lance, Ilana, and Octus go deep in to the swamp to find a Mutraddi that has landed in the water. They investigate the crashed ship 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 kill the original Mutraddi beast, turning Ilana back to herself.
Muculox, a frog-like Muttradi, crash landed on Earth, in a swamp, engaging Lance, Ilana and Octus as they came to investigate. After being electrocuted by Octus underwater he is apparently killed and thrown on shore. While discussing what to do with the beast, Muculox revives and wraps his projectile tongue around Ilana's ankle, giving her a topical venom burn before fleeing into the swamp. This venom burn slowly infects her and begins to replace her DNA with that of the creature's, making her stronger and more nimble, as well as altering her appearance. Midway through her transformation, Ilana encounters a dead alligator that shows some of the same transformation signs as she has: webbed hands, and light greenish skin, and two eyes on its bottom jaw in addition to its own eyes. The mutant alligator also revives from its deceased state and attacks Ilana. She manages to survive being bitten by the giant creature with little to no injury, and the beast is killed when Ilana snaps the mutant gator's jaw. Realizing her transformation is rapidly progressing, Ilana escapes from Lance and Octus, going deeper into the swamp. The duo soon catch up and find her mind under Mucolox's control. Walking towards the two with Mucolox watching nearby, Mucolox then emits a call from its vocal sac, causing Ilana's eyes to change, before she rips off her clothing and completes her transformation. This call was also used to summon his ship from where it rested at the bottom of the swamp, so he could take Ilana back to Mutraad and gain an even greater reward for bringing her in alive. However before they could leave, Lance kills Muculox by using the Manus armor to leap up to the escaping ship and stab a Triton through Muculox's chest, piercing its heart. When Muculox dies, the ship crashes and the psychic link between Ilana and Muculox is severed. Ilana goes into cardiac arrest for a period of time, but then her mutated heart restarts. With the link now severed, she reverts back to her humanoid form and Lance put his sweater on her (because she's nude). Discussing by a campfire that she wants to go on a date when they get home, Lance says she might want to wait. Ilana asks Lance why that is but he just asks for Ilana to trust him.
- This is the first episode where Lance is seen wearing something besides Galalunian clothes or his standard outfit for the majority of an episode.
- Ilana mentions a 'Prince Simon of Duran'. This is a reference to Simon Le Bon, lead singer of 80s pop band Duran Duran.
- After Ilana was transformed into a creature, she still wear pieces of her clothes but seconds later they vanished without ever sigh of them falling or being ripped off.
- When Ilana attacks Octus, her ripped white jeans reappear for a moment.
- Just as Ilana notices that her hands are changing and she jumped off of the log she was on, her shirt is the same color as her jacket for a couple of seconds.
- When Ilana turns back to normal, her leg injury (which she got from Muculox) is gone, it is possible that it healed in the transformation.