Currently going thru making a tier list, and it's taking a long time due to a lot of thought being put into it, but I've made a small sampling of what I have devised definitely:
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What I am doing is making a chart of the 51 official playable characters in the series (Dr Mario omitted, 3 different Links: OOT/MM, TP, and WW/PH, each relegated to items from those games)
Also some blanket rules I'm using:
-No healing/magic restoring items unless they have a function other than just healing (eg. Falchion)
-Vehicles can only be used if the opposition has vehicle as well (exceptions including but not limited to Meta Knight using the Halberd, Pit using the GST, Rosalina using the Comet Observatory, Fox/Falco using the entire Great Fox, etc)
-Power ups/items can only be used once each (Fire Flower, Power Pellets, Bag of Dragonite, Mega Lazer, etc) or dependent on ammo/magic (bombs, Metal Blade, missiles, PK Love, etc)
-Sending opponents away DOES NOT count as victory (eg. Mewtwo erasing Ganon's memory then warping him to Oklahoma)
-Pokémon not owned by Pokémon Trainer are wild, no ev's, no items (unless held in wild eg. Light Ball), and can only use learned moves and egg moves (no TM, HM, breeder)
-Eating challenger for OHKO (Kirby, Dedede, Yoshi) is prohibited
-No assistance from other beings (Wisps, party members, summons) sans Ice Climbers, Olimar, Rosalina, Pokémon Trainer, etc
This might take awhile, but are there any objections so far?