In every Pokémon game I have 20-30 Pokémon that can and mostly will feature at some point of the story. But my favourite 4-15 Pokémon invariably get the most face time:
I've also always avoided using legendaries and mythics in my teams mostly because I rarely liked many of them. Notable exceptions are Zapdos in Gen 1, Raikou and Celebi in Gen 2, Jirachi in Gen 3 (also used Kyogre as an HM slave but meh) the lake trio and Cresselia in Gen 4 (though I didn't like Gen 4 much, least favourite gen overall - I legit released Palkia/ Dialga) Zekrom, Virizion, Cobalion, Meloetta, Genesect and Keldeo in Gen 5, (holy crap Gen 5 was goooood! - especially considering it has 2 of my favourites in the spoiler) Yveltal in gen 6 and Tapu Lele in gen 7.
Out of all the legends and mythics, the only one that has ever been central to any of my strats was Cresselia. So I guess that's a redeeming quality of Gen 4.
As for multiplayer, I like doubles a lot, so typically my most played Pokémon is sky drop Aerodactyl as he's such a useful partner for just about any other Pokémon I use.
EDIT: In terms of complexity, I think the most roundabout strategy (short lived as it was) I've used was one that involved skill swap and Reuniclus, though that's all I remember from it. It was powerful but not enough to validate the hassle haha
