Howzabout this: Not Larry Nice
Foul Larry has moved into Fosters, but he and Wilt don't get along. Larry still hates Wilt, and Wilt still hasn't forgiven Larry after all these years. (yeah, I know he's Wilt, but just think of the trauma! Even Wilt would be hard-pressed to forgive him

)
So, Mac thinks that they should be freinds, after all, Larry's trying to be a good person now, and it pains Mac to see Wilt all riled up like that.
So, he tries, and fails, so he and Bloo go around asking all the people in the house how they make friends with people. Eventually, Frankie tells them to find something they have in common. Bloo recognises that they both share the love of basketball, so challenges Foul Larry to a game of five-on-five basketball using his freinds as teammates.
But Foul Larry raises a team of the biggest, tallest imaginary friends in the house (including the New Guy) to take 'em on. So who will win, and, more importantly, will the Fosters Five even survive the match?
Gags:
Not many yet, but one where Bloo says to Mac:"Well, duh! We're in a house FULL of creatures who were MADE to be freindly! One of them HAS to help us get them to be friends!"
Then cut to a scene of Duchess telling Mac and Bloo to "Go away."

. Bloo turns to Mac and says "That first one doesn't count."
Also, Mr Herriman suggests a game of cricket, but Bloo misinterprets it to mean he should dump a load of crickets on Larry. "Did you see that? Nothing. Do you know how long it took me to find all those crickets?!"
This is meant to be a comedy episode, eith some exploration into the relationship between foul Larry and Wilt. I would turn this into a fanfic if I had the time. What do you all think?