the Japanese openings have spoilers, as well (though none as spoiler-filled and badly timed as the Pokemon Advanced Challenge opening... for god's sake, Ash didn't even catch Torkoal when the dub started playing that). "Mezase Pokemon Master" showed Satoshi releasing a Pigeot to battle an Onidrill (oddly enough, he only has Pigeot for one episode, and it evolved the episode right after the theme changed). "Rival" seemed to indicate that someone would be getting a Laplace a few episodes early.... Kabigon also appeared in the beginning, but I don't know if that should count (the beginning of that opening also shows a Rarecoil, a Yadoking.... and that over-showcased piece of crap, Guardie.... which kinda pop out of nowhere).
"OK!" showed Chicorita, Hinoarashi, and Waninoko with Satoshi, as well as that Bulu with a taste for Nyaasu's tail. Heracross appeared in the opening as well, but like Kabigon in "Rival", his presence is diluted by the fact that said scene also featured a Ledyba and a Hoho (although, Pikachu was the one riding it, and it did get a brief scene of it unfolding its wings, unlike the other two). "Mezase Pokemon Master 2001" showed Bayleaf several episodes too early. Crobat also made an appearance, but once again, it wasn't part of the team, but shown with several other random Pokemon. "Ready, Go!" showed Yougiras with Satoshi and all of his Pokemon (which, interestingly enough, included Lizardon, but no Zenigame... Betobeton and Kentauros were absent, as well). A brief appearance by Nyorotono, but once again, the appearance was random and not included with the main characters. Nanako also made an appearance with Satoshi's other rivals, Shigeru and Hiroshi... this was either indication that she's one of his mainstay rivals now, or this was little more than foreshadowing that she'd appear again in an upcoming episode (if they were telling us she's one of his main rivals, it sure went nowhere fast.... poor girl's been forgotten since Housou).
"Advanced Adventure" featured Satoshi with Subame and Kimori, Haruka with Achamo and Agehunt, Takeshi with Mizugorou and Hasubou, and Rocket Dan with Habunake and Sabonea. The ending theme "Smile" was the first ending theme that got updated to fit any changes to the team. "Challenger!!" featured Oosubame, Wakashamo, and Fushigidane (though, not many people could tell that it'd be Haruka's). Another ending, "Glory Day", featured Runpappa and Yukiwarashi, and like "Smile", it also got updated (though, a couple episodes after said updates take place) to feature Haruka's Gonbe and Satoshi's Onigohri. "Glory Day" also featured all of Satoshi's Pokemon, including the ones he released, but despite endless speculation, they didn't end up returning. "Pokemon Symphonic Medley" didn't feature any spoilers (though, Runpappa and Yukiwarashi are seen together, but it was in another scene with several other Pokemon. A Gonbe makes an appearance, too, but nothing to indicate Haruka getting it).
[spoil]"Battle Frontier" spoiled us on Manene (in a Rocket group scene, though. Kojirou's ownership wasn't specified), as well as Usohachi (Masato was featured in the scene along with Takeshi and his Pokemon, though, so people speculated that it'd be his first Pokemon). Manyula briefly appeared at the end of the afforementioned Rocket group scene, likely as a movie plug, and to this day, people are still under the impression that Musashi or someone in Rocket Dan will get the damn thing. This opening also revealed that Shuu would continue being Haruka's rival, to be expected, but also Harley, which was a bit of a surprise at the time. Like "Smile", this was also updated to suit the addition of Haruka's Eievui, as well as the evolutions of Numacraw, Donphan, and Jukain. At some point, Dokucale was also added into the Rocket group scene (it was mysteriously absent earlier), and oddly enough, Chiriin remained. The current opening, "Spurt!", much like "Glory Day", features all of Satoshi's and Haruka's Pokemon, whether they're currently in custody or released (we even see the Yougiras that Satoshi took care of at the end of Jouto). Again, there's no true indication that any of those released Pokemon will be making a comeback. This opening's been updated as well, but not to suit party changes. Rather, a scene with the Battle Pyramid at the end was replaced with a plug for Pokemon Ranger. We have yet to see if this opening will have any party updates, because thus far, no changes within the party have occured.[/spoil]