Season X is a special season of Phineas and Ferb. It involves the future (like in Phineas & Ferb's Quantum Boogaloo) but with some changes.
Changes from the future from real P&F
- Doofenshmirtz was turned into Dr. Shadowshmirtz and lives in an alternate dimension called Dimension X (hence the season's name)
- Agent P is not old, and he ran away from the Flynn-Fletcher family reluctantly because he needed to go to Dimension X to stop Dr. Shadowshmirtz.
- adult Jeremy, adult Phineas and Ferb, elderly Dad, aunt Isabella, etc. appear
- Meap, Mitch, and the rest of the aliens appear regularly (more than Perry and Dr. Shadowshmirtz)
- Xavier and Fred have a pet named Carl the Cat, who is actually Carl the Intern who got turned into a cat by Mitch