Trade-Off

Trade-Off is the thirty-seventh episode of Ben 10: Alien Force.

Plot
Kevin barges into Darkstar's hideout. As they rumble Darkstar offers a partnership where both of them will regain their original appearances. He explains that a mystical artifact called the Dominus Librium has the power to transfer energies in order to balance them thus returning the object to its previous undamaged form. The artifact is located in an dangerous island filled with traps. They go to the island and eventually get the artifact.

Meanwhile, Ben and Gwen try to contact Kevin for a mission. He doesn't answer making just the two of them to go on. After using the artifact, Kevin loses his powers and regains his human appearance as does Darkstar. He sucker punched Kevin and keeps the artifact as he retreats. Kevin returns shocking Ben and Gwen who sensed his regular skin. He doesn't tell about his alliance with Darkstar. The trio fights off some Forever Knights in which at first Kevin should've stayed in the car. He comes in and helps them fight anyway.

As he drops the Tennysons home, he asks Gwen if she liked to go out with him. Gwen declines as an image of Darkstar appears instead of Kevin. Due to this, Gwen finds out what he did and goes to fight Darkstar, but Michael uses the libruim and starts absorbing her energy. Kevin and Ben come to help but Darkstar absorbs Ben's energy as well. Since Kevin can't do anything he grabs the librium which overloads and explodes. Because of this, Kevin was turned back to his previous mutation as it's the same with Darkstar who vows to get revenge. Gwen tries to apologize to Kevin but he says it's fine, as it was his fault and it wasn't worth Gwen's safety. Then, Kevin, Gwen and Ben go to Mr. Smoothy.

Major Events

 * Darkstar returns and makes an offer to Kevin to return to their original forms.
 * Kevin returns to his human form but loses his powers.
 * Kevin reverts back to his mutated form.

Characters

 * Kevin Levin (main character in this episode)
 * Ben Tennyson
 * Gwen Tennyson

Villains

 * Michael Morningstar
 * Forever Knights

Aliens Used

 * Jetray
 * Big Chill (accidental transformation; selected alien was Humungousaur)
 * Echo Echo (accidental transformation; selected alien was Jetray)
 * Swampfire

Errors

 * When Ben turns into Jetray to go to the Forever Knights' hideout, the two black stripes on his shoulders are missing for a few frames, just before he picks Gwen up from the ground.

Trivia

 * The background music in the temple when Kevin and Darkstar take the artifact is the same music as in Ben 10 Alien Force: The Rise of Hex.
 * Jetray's voice sounds extremely similar to Stinkfly in this episode.