[His face falls. He really should've expected that this might happen if Mabel showed up again.]

Annnnd you don't remember.

[But hey, what's a few memories? It's better she's here without remembering than not here at all.]

Okay. Okay. You know what? I can work with this.

[He just has to figure out quick way to explain everything.]

A giant space worm is going to destroy all of existence, so this cosmic time being -- that isn't a baby -- called the Time Trapper, keeps pulling people to an alternate future universe filled with superheroes and giving them superpowers. To fight the giant space worm.

Which is why I'm dressed like this.

[He gestures to his costume]

The Time Trapper threw us into this weird scenario because he make these dimensional bubbles, or whatever they are, to test people.