Phineas and Ferb Save Summer, on Disney XD & Disney Channel
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This hour-long special first aired in 2014, during season 4 of Phineas and Ferb, but I didn't see it until 2023, on Disney+.

Phineas, Ferb, Buford, Isabella, and Baljeet are putting on a concert in their back yard, which they're using holographic technology to broadcast all around the world (with differently-dressed avatars of themselves in each country). Meanwhile, Major Monogram gets fired from the O.W.C.A., and is replaced by Carl. Dr. Doofenshmirtz creates an -inator to move the Earth farther from the Sun, which ends summer. So Phineas and the gang leave the concert in the hands of Irving, while they investigate what's going on. Phineas and Ferb's parents go spelunking. Candace has to try to overcome her fear of spiders. The gang comes up with a plan to move the Earth back to where it belongs, with help from kids like them around the world. Doofenshmirtz and the other evil scientists of L.O.V.E.M.U.F.F.I.N. capture almost every OWCA agent, leaving Carl, Perry, and Monty to try to stop the villains themselves. And a bunch of other stuff happens, and eventually the day is saved. And I really enjoyed the way in which Major Monogram became the head of OWCA again. I don't feel the need to go into any more details. It was a reasonably fun and amusing special, but I didn't like it as much as some other specials, and I don't know why. It was definitely good, though.