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Atk, SpAtk, Def, SpDef and speed increase by 6% in Hail for Ice types
Hail can be stacked by a Snow Warning user. icy rock doesn't effect the number of turns added when stacking.
Stantler, Delibird and Uxie get Snow Warning
Snow Warning also gives immunity to Hail Damage
Drifblim, all Pranksters and Overcoats get Hail
Stealth Rock gets halved
All cocoon pokemon get Rapid Spin[so butterfly evolutions do too], Voltorb, Shuckle, Snorunt, Drifloon, Bronzor, Lickitung, Venipede, Tirtouga, Trubish, Paras, Klink, Chespin, Lotad, Ferroseed and Bonsly families get rapid spin through various methods.
Rapid Spin gets 60 BP
Gyro Ball acts as Rapid Spin if the user is faster than the opponent
Airlock and Cloudnine completely eliminates weather
A new weather can be used in conjunction with Hail, called Snow. Snow weakens the power of Steel, Ground and Rock type moves and increases the power of Ice type moves. this is an 8 turn move and can be increased by the icy rock to 12 turns,
Fairy resists itself
Ice takes neutral damage from Fighting
Fairy stops resisting Bug
Steel stops resisting Psychic
Poison type move that's SE against Steel