Effect Spore in Pokémon Black & White

Contact may poison or cause paralysis or sleep.

Has a 30% chance of inflicting either paralysis, poison, or sleep on attacking Pokémon on contact.

Whenever a move makes contact with this Pokémon, the move's user has a 30% chance of being paralyzed, poisoned, or put to sleep, chosen at random. Nothing is done to compensate if the move's user is immune to one of these ailments; there is simply a lower chance that the move's user will be affected.