This series does this logistically, by having Yuto/Kamen Rider Zeronos kidnap Ryotaro/Kamen Rider Den-O three times in episode 25 and 26, and take them all back in time to the Edo period to fight Kamen Rider Gaoh, all without Ryotaro having any memory of the event. But Kamen Rider Gaoh doesn't actually start his evil plan until episode 27, which leads right into The Movie, which ends with Ryotaro almost beaten by Gaoh, until Zeronos shows up at the end with the three past versions of Ryotaro, allowing him/them to activate all four of his armor forms at once. In short, they used time travel to stop the evil plan and did so before it happened. One of the best uses of time travel in any series, ever.
Liner Form's debut. Ryotaro himself takes out two Imagin who formed a drill-like twister with a Denliner shaped attack.
Kotaro/New Den-O and Teddy's arrival by destroying an Imagin in 8 seconds, and they made sure to count it themselves.
In part 2 of Ryutaros' debut, fighting two Gigandeaths by summoning Ikazuchi and then combining all of the DenLiner cars for battle for the very first time. Even better, Den-O pilots the whole thing from the outside, riding on Ikazuchi's head!
Episode 3 (or was it 4?). Momotaros has teamed up with a dude stealing from a criminal organization - partly for the chance to fight, partly to pay back Ryotaro for the threads he'd bought while posessing him - and when Ryotaro wakes up, he is having none of it. He forces Momotaros back to the DenLiner, and tells him not to come back unless summoned. Then an Imagin shows up, and Ryotaro in Plat Form gets his ass kicked, naturally. Thing is... he keeps getting backto his feet and trying, despite his poor reflexes and sloppy form. Momotaros starts yelling at Ryotaro to let him in and become Sword Form, or else Ryotaro's going to get killed. He doesn't care, because he refuses to work with a thief, and gets Momotaros to not only incoporate some standards, but also to apologize. And then, the two work together to Curb Stomp the Monster of the Week.
Episode 18. An imagin has been rampaging for the last episode and a bit aimlessly, while Ryoutaro and the others sort out problems and such. Ryoutaro fought it in Plat Form which, as per standard, was a Curb-Stomp Battle against him, the Imagin managed to dodge Ryuutaros's finisher... then, once problems are resolved for all but Momotaros, who's a little pissed off that he was worried for no real reason, they fight the Imagin. Rod and Axe form both fight the monster, and trade blows, although they do pretty well, and Kintaros was going to finish it, Ryoutaros has them switch to Sword form, give Momotaros a turn. After being knocked around because Momotaros isn't even pretending to fight, Momotaros resolves his problems with Ryoutaro... and then proceeds to Curb-Stomp Battle the Imagin right back, just striking him over and over with sword slashes, not getting hit once, then ending it with a new finisher which segueways into a Funny Momoment.
Many people talk about the running gag that female riders tend to die as quickly as they appear with very few exceptions, though no one talks about how every movie rider has a tendency to die. Granted, most of them filled the role of villain, but even the heroic or anti-heroic riders get killed off too (with the possible exception of the Oni in Hibiki... provided you discount "dying of old age" as the cause of death). Enter New Den-O, who ends up surviving the events of his movie and many more movies to follow, marking him as one of the first. That's pretty awesome.