Phineas and Ferb: Battle Beyond Dimensions

Phineas and Ferb: Battle Beyond Dimensions is an upcoming fan fiction by Tennantfan.

Synopsis
Phineas and Ferb are having an ordinary day, building a gateway allowing them to travel across Dimensions. But when they finish, a dying Phineas emerges and warns them of an evil villain that is dominating all dimensions, one by one. So now it's up to that version of Phineas and Ferb to travel across the Dimensions and meet up with themselves, as well as some other allies in order to save all the other dimensions.