I am a Changeling Polymorph. I can take the form of anyone.
~ Otto Scaarbach revealing his shapeshifting abilities.
Otto Scaarbach is a supporting antagonist in the Tales of Arcadia franchise, appearing as a supporting antagonist in the first arc, Trollhunters, and a cameo character in the second arc, 3Below.
He is a Changeling Polymorph, and as such, could take the form of anyone without the need of a familiar. He is also the Grand Commandant of the Janus Order, a secret global organization under the guidance of Morgana that awaits the return of Gunmar by freeing him from the Darklands.
Otto is first seen with an unnamed customs agent and shows her that he has the Eyestone, the last piece needed to complete the Killahead Bridge. He brings it to the museum, and the bridge is completed. However, Team Trollhunters is able to interfere before Gunmar is released.
After that incident, Otto goes directly to Stricklander, and they travel to Asya-Thoon where Angor is chained, and Stricklander awakens Angor Rot and put him under his control. Otto questions him controlling the legendary assassin.
Eventually, Otto discovers Stricklander's plans of leaving Gunmar behind so the Changelings can rule the world from the shadows instead of Gunmar. He tells the rest of the Janus Order about this, and even though he knew Angor Rot was out of control, he abandons Stricklander and leaves him to die.
Toby, Claire, Blinky, and NotEnrique find Otto but are unable to track him to the Janus Order's base. However, Toby's dentist puts a unique headgear on him that can pick up radio signals. The headgear soon picks up signals of the Janus Order. The team is able to discover that the secret base is five stories beneath an abandoned travel agency named Omni-Reach Travels. Upon entering, they are eventually captured by the Janus Order and interrogated by Otto Scaarbach himself, who takes off Toby's headgear to keep the team from spying on the Janus Order further. During the interrogation, Otto also briefly listens to the phonograph which Morgana speaks through. He then offers a trade to the team: the antidote to reviving AAARRRGGHH!!! for Vendel's staff.
Eventually, Toby uses a Glamour Mask to disguise himself as Vendel to take his staff. Beneath the bridge, the team gives Otto the staff, and Otto gives the ingredients for the antidote to the team. With the said list, they are able to get all the ingredients and revive AAARRRGGHH!!! from being a stone statue, and thus, Otto honored his part of the deal. Otto also gives Vendel's staff to Gunmar once he is unintentionally released from the Darklands by the current Trollhunter, Jim Lake Jr.
Otto also develops a rivalry with Dictatious Maximus Galadrigal in becoming Gunmar's favorite minion, but this rivalry soon ends when Gunmar, having no more use for the Janus Order, massacres them and brainwashes Otto into disguising himself as Gunmar before leaving to Trollmarket to build a new Gumm-Gumm army with Queen Usurna. When Team Trollhunters arrives, "Gunmar" appears and tries to kill them, only for Jim to slash at his side. However, it's revealed that it was Otto brainwashed by the real Gunmar, who reveals that they've fallen into his trap, shortly before Otto explodes into smithereens.
In Part 1, Otto briefly appears in a recording where he is fighting Jim while disguised as Gunmar.
Despite being a Changeling Polymorph, he is never seen in his true form.