Drizzle: Upon entering battle, the weather becomes rain (For all Pokémon on the field, Water-type moves deal 1.5x damage and Fire-type moves deal 0.5x damage).
Simple: Its stats are twice as affected by modifiers (Swords Dance raises 4 ATK stages instead of 2, Tail Whip lowers 2 stages instead of 1, etc).
Unaware: During damage calculation, ignores foe's stat changes except SPEED.