Weapon F

Phineas, Ferb, and the gang all get the powers of the X-Men. They must team up with Candace, Stacy, Jeremy, Professor M (Monogram) and The Mechanic (Carl) to stop Tin Can (Doof) and his daughter ChickMagnet (Vanessa) as well as the Buggernaut (Buford)

Heroes
Phineas + Wolverine = Weapon F

Ferb + Nightcrawler = Nightwatchman

Isabella + Storm = Rain

Baljeet + Beast = Hanuman

Django + Gambit + Masterpiece

Irving + Jean Grey = Jean Geek (he gets Jean's hair as well)

Carl + Forge = The Mechanic (prosthetic leg as well

Monogram + Xavier = Professor M ( wheelchair and baldness as well)

Stacy + Jubilee = Spark

Jeremy + Cyclops = Patch

Adyson + Kitty Pryde = Lady Phantom

Perry (no powers)

Candace + Rogue = Solo (neutral)

Villians
Buford + Juggernaut = Buggernaut

Vanessa + Polaris = ChickMagnet

Doof + Magneto = Tin Can

Norm (no powers, but later Doof uses his powers to make Norm 20 ft. tall)