Master Control

The Master Control is a program found in the prototype Omnitrix, Ultimatrix, and Omnitrix. It adds great powers like access to aliens in Ben 10: Alien Force and instant changes just by thinking and unlimited timing in Back With a Vengeance. It can be unlocked by a special code or voice command by Azmuth, as seen in War of the Worlds: Part 1 or in a rare cases by hacking, as seen in Inspector 13.

Original Series
It first appears in Back With a Vengeance. Ben unlocks it by using a combination/code when on a boat trip. When a man falls off 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 gets the Omnitrix 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.

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 aliens 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 Omnitrix still powered down when Ben rapidly depleted it of all of its power faster than it could recharge by turning several DNAliens back into humans from a distance. It is also revealed that he will still revert back to human if knocked unconscious.

Ultimate Alien
The Master Control is unlocked in Inspector 13, this time on the Ultimatrix. It was activated via hacking when three firewalls were breached.

In The Ultimate Enemy: Part 2, Azmuth confirmed that the Omnitrix also has a Master Control when he said he might activate it on Ben's 18th birthday.

Trivia

 * Dwayne stated that Ben could unlock the Master Control via Voice Command, but he'd have to unlock it manually first.
 * The Master Control was unlocked during the second seasons of the Original Series, Alien Force and the third season of Ultimate Alien.
 * Even though the names by which Ben calls his aliens are made up, the Omnitrix recognized them when the Master Control was unlocked.
 * Ben showed off his understanding of the Omnitrix and his skill of adapting as he used the Master Control without difficulty in Back with a Vengenace