This takes place during season 3 of II (inanimate insanity invitational) and paintbrush had come back.
Also in this AU another one of my ideas is canon (lightbulb's folks) if you don't know what that is i recommend you go back in the book now on to the show!
Lightbulb has been having constant nightmares ever since paintbrush left she thought after they came back but the nightmares have only gotten worse they've gotten so bad that the other hotel guests (since Mephone4 isn't doing season 2 at the moment he decided to let the contestants stay at hotel) are starting to notice her almost self harming behavior like her falling asleep at the stove while it's on or burning herself with coffee (she didn't drink coffee before the nightmares). They're not sure what to do so lightbulb, fan, and paintbrush go into testtube's "secret" lab to try and find something to help and they find "the dream machine!" A Device which allows a object to go into another objects dreamscape!
They hook lightbulb and paintbrush up to the machine while fan makes sure everything goes fine :)
While there in lightbulbs mind they see her fears, trauma, suicidal thoughts, crush's, the mental representation of her depression, and other stuff you'd think you would see In a mind! They also keep being chased by the thing they have to get rid of "the nightmare!" And when they do eventually kill it it turns into paintbrush which confused the real paintbrush for a minute before lightbulb explained that she was afraid of them abandoning her again.
As for the ending and the stuff in between that's up to you guys! Now I hope you all enjoyed this AU idea and someone uses it now marry Christmas and happy new year!!!