In some alternate future universe, Leo and Yuichi Usagi bring out each other's brand of stupidity that doesn't go away with age, despite both of them having grown into their roles as group leaders.
You know how Leo loves magic tricks and can pickpocket stuff with his sleight of hand? The turtles and Usagi's group end up fighting each other, and midway in the fifth, Leo somehow got Usagi's yoyo.
"This looks mystic, what's this?" Leo smirked, brandishing the yoyo up and out of Usagi's reach as soon as the rabbit was too close for his dual swords.
And Usagi, despite growing up to five feet as an adult, barely reached the blue turtle's shoulders. "Give that back!" he demanded, doing the first thing that came into his mind: he jumped up and hit the top of his head under the turtle's chin.
They both staggered away from each other from the crash. The others stopped their fighting to see the spectacle: Leo having been hit in the stupidest way possible, and Usagi having hit the enemy in the stupidest way possible.
"Ow! You just made-th me bit-th my th-ongue!" Leo yelped, holding his chin.
"Your chin hurts! I know your jaw is big, but still!" Usagi complained, holding the top of his head.
When the misunderstanding cleared out of the way and the two groups became friends, Leo never lived down Usagi's chin attack.
"Yeah, like when you Mario-jumped me on the chin?" he'd joke.
"And it felt like bricks too," Usagi answered frankly in his unassuming manner of his.