Version 1…
All of the cast of Foster's are sitting in the foyer; all of a sudden a vortex swallows Mac and hurls him into the Powerpuff Girl universe. After the girls have their way with him he looks like a Powerpuff Girls reject.
Version 2…
Before Bloo goes to Foster's to live there is an incident… Bloo and Mac are playing a game… "Throw it here Bloo!" a bowling ball flies out of nowhere at Mac and gets lodged in his head. After many attempts to get up and talk he finally manages to ask where he got that bowling ball, the world may never know…
Version 3…
When he was younger…
"Mac stop that now!" his mother yells at him.
"Never!" he yells while jumping on the bed. After hitting the ceiling somehow he falls on his head and it swells to the size of a watermelon, at this point Bloo is "born".
Version 4…
You see the Trix rabbit stealing Trix cereal from a herd of ankle biters (small children). "Hey you!" Mac yells, "Trix are for kids!"
"You'll never take me alive you little Insert Curse word here ." The Trix rabbit shouted back as he hopped on a truck to make a get away.
"You won't get away that easily." Mac smiled. He kicked one of the ankle biters off of a trike and somehow, by the power of fanfiction, managed to catch up with a truck that was going 60mph. After a daring fight that got them to the top of an office building, "No! Don't!" Mac yelled desperately, but it was too late.
"Ha!" the bunny laughed as he ate the Trix cereal. A sickening crunch was heard and Tony the Tiger appeared out of the shadows.
"Hey Tony! You're out of rehab early!" Mac said gleefully as he stepped over the killed off rabbit.
"Yeah, well, I got off for good behavior." He glanced at the rabbit. "Good thing I got here in time, if he had eaten all of the Trix, the world would have been doomed."
"How?" Tony leaned over to him and whispered in his ear something so shocking that the impact of it made Mac's head swell up.