Master Control

The Master Control was a program found in the Omnitrix and confirmed by Dwayne McDuffie, in the Ultimatrix. It adds great powers like access to aliens in Ben 10: Alien Force, and instant changes and unlimited timing in Back With a Vengeance. It's unlocked by a special code or voice command by Azmuth.

Original Series
The Master Control first appeared in the episode A Small Problem, where Ben is stuck as Grey Matter. He failed to turn back until the Master Control zeroed out. It reappears in Back With a Vengeance. Ben unlocks it by accident when on a boat trip. When a man falls of the boat, he uses Ripjaws to get him out of the water and Stinklfy to fly on back to the boat. He then stays Stinkfly for hours (showing off his unlimited timing) and ruins Gwen's ice cream, who's extremely annoyed by his new powers. After this, he ruins some pictures and causes more trouble until Vilgax and Kevin 11 come to steal the Omnitrix, until Grandpa Max sends them into the Null Void with Ben as Diamondhead. After a long chase, they finally get the Omnitrix until Gwen tricks them and get them back. But Ben, who turned off the Master Control, accidently transforms into Grey Matter and tries to turn back but fails. While it was the last time seen in the first series by Ben, it makes another appearance in Ben 10,000 and Ken 10, being used by the future Ben repeatedly and later also by his son Ken.

Ben 10: Alien Force
The Master Control reappears in War of the Worlds when Azmuth activates it by voice command to grant Ben all of the Master Control abilities from the original series as well as unlocking every single alien in the Omnitrix. He used alien from the original series such as Upchuck, Way Big and Cannonbolt (and Wildmutt offscreen as confirmed by Dwayne Mcduffie). After the Master Control was deactivated, these 4 aliens were appended to his Alien Force list of aliens which he used throughout Season 3. However, the Master Control is not limitless, as overexerting the Omnitrix's energy will revert Ben back to human form as seen when Ben used all its energy to restore several DNAliens to human. It is also revealed that he will still revert back to human if knocked unconcious. In Con of Rath, a Tiffin accidently unlocks Rath and Master Control forces Ben to stay as Rath. When he is seperated from the Tiffin, he changes back to human.

Ben 10: Ultimate Alien
Dwayne McDuffie confirmed that the Ultimatrix also has the Master Control. It's currently unknown if it unlocks more aliens or the powers from the original series.

Trivia

 * The Master Control unlocked in season 2 finale of Original series and Alien Force, possbily unlocked in Ultimate Alien Season 2 finale.
 * Both times that Ben unlocked the Master Control he became Cannonbolt.
 * Possibly the next time Ben unlock the Master Control he is transformed into the original series aliens, aliens from Ben 10,000 (Articguana, Spitter, or Buzzshock) or other aliens in Condon Stream (Highbreed, Chimera Sui Genesis, or Osmosian).
 * Ben used it twice to defeat the main enemy of the season (Vilgax in the original series and the Highbreeds in Alien Force).
 * Logically, Ben could re-unlocked the Master Control by using brainpowers of his smartest aliens, such as Grey Matter and Benvicktor (in the original series) and Brainstorm (in the Alien Force series). This can be seen in the episode Ken 10, where Ken uses Grey Matter's intellect to unlock the Master Control. If Ben thinks of this, then he and Kevin didn't have to hack the Omnitrix in Vengeance of Vilgax Part 1.