The Nikola strategy does not work because the Arceus uses Extreme Speed and onehits the Seaking but I managed to setup Azumarill with three Def. Curls and it was finished by toxic (My Forretress has Toxic Spikes cause I never use Gyro Ball, and I could set up on Mewtwo fully (Sr, 3 Spikes and 2 T. Spikes). After Arceus fainted Deoxys used Engergy Ball and boosted my Atk. three times and I killed the Dragonite with 2 Play Roughs. Other strategy is to setup Forretress first and then setup Snorlax (u need a few Max Potions). Sorry if there are a few grammar mistakes my english isnt the best.