The Beige Guardian, apparently a Guardian of Time and peer of the Black and White Guardians, was actually a character from Happy Deathday, a video game Izzy Sinclair played on the Time-Space Visualiser.
In this game, the Beige Guardian collected every enemy of the Doctor's and then the first eight incarnations of the Doctor. The Guardian tied them up and placed them on a huge cake with hissing dynamite "candles" strapped to their heads. The Beige Guardian announced the Doctors would be forced to face every enemy they had ever defeated at once, a task the Doctors found tedious.
Leaving the First and Eighth Doctors tied to the cake, the Beige Guardian sent the rest to battle their collected enemies. While the Guardian was distracted and dismayed by the Doctors' victories in the battles, the First and Eighth Doctors worked together to break free of the cake. They used a giant fork to launch an exploding candle at the Guardian, which disintegrated him.
All the other Doctors reappeared by the cake. The First and Eighth Doctors explained their deduction that the Beige Guardian had been merely a collection of electronic impulses, easily dissipated by the explosion. The Doctors began questioning the nature of their own existence. What if they were all just electronic impulses arranged for someone's amusement? Watching the exchange on the Time-Space visualiser, joystick in hand, Izzy grinned at her video game. (COMIC: Happy Deathday)