An extremely useful move in the video game, Pokémon. Haze removes all temporary stat modifiers from both Pokémon currently in battle, and all status modifiers from the creature using it. As such, it can sometimes even work against the attacker.
Stat increasing moves such as the attack power boosting Swords Dance, the defensive Acid Armor and the infamous evade-increasing Double Team are cleared from both creatures. Stat-lowering moves such as Screech and Growl are also negated. Additionally, if the attacking Pokémon is suffering from Poison (including Toxic Poison), Paralysis, Confusion, Burn, these are cleared too.
The main purpose of a "Hazer" such as Vaporeon is to annoy an opponent whose movesets rely heavily on stat-boosters, most notably Scyther's infamous Double Team/Swords Dance combo and Snorlax's Belly Drum. It's also effective against status-inflicting movesets such as the Death Starmie.