Now that DP remakes have been confirmed, I think it's a good time to look back to 2010, back before Dynamax, Z-moves, and Mega evolution, back when Pokemon games were still named after minerals, back when Mindy hated you so much that she actively avoided giving you a Gengar, and play the
Generation 4 Sinnoh Tournament
All battles must be played in gen 4 OU. This means using gen 4 mechanics, and Garchomp and Manaphy are banned.
You can use a Pokemon only if it's introduced in gen 4 OR on the Sinnoh Pokedex. For example, Heatran and Scizor are both allowed.
Additionally, I want to ban stealth rock, but I'll let participants vote on that.
Based on this allow list and the gen 4 OU viability rankings, the top 26 Pokemon in this tournament will probably be Heatran, appliance/alternate Rotom, Infernape, Clefable, Gyarados, Gliscor, Gengar, Bronzong, Empoleon, Magnezone, Machamp, Lucario, Roserade, Azelf, Milotic, Blissey, Uxie, Hippowdon, Scizor, Heracross, Shaymin, Mamoswine, Abomasnow, Crobat, Togekiss, and Quagsire.
I recommend reading these resources if you do not have much experience playing with gen 4 mechanics.