Mxyzptlk and The Dodo using their powers to get the toons into the real world; in the end, Mxy tried to fuse both worlds, and it was Bugs who saved the day by tricking him into saying his name backwards.
Well, at first they got a bit shocked, especially when some of them got the superheroes' powers for a short time; Elmer became Superman, and Daffy became Batman.
Later, the heroes and toons worked okay together. Besides Mxy and the Dodo, they also had to fight Toyman, who got several giant robots thanks to Mxy's help, and the toons made a good job assisting the heroes; Tweety got inside a robot's system and made it dance Macarena instead of fighting, and Bugs tricked Taz into eating another robot. When Batman congratulated Bugs on the victory, he said that was even more manipulating that some stuff he (Batman) has done in the past, and Bugs says...
"Heh, ya say dat only because ya didn't t'ink it foist."