Generation Iii
Effect Spore
Leaves spores on contact.
Detailed Effect
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.
Pokémon With Effect Spore
11 canonical Pokémon forms can have this Ability.

Paras
Parasect
Shroomish
Breloom 
Foongus
Amoonguss
Morelull
Shiinotic
Vileplume
Gossifleur
Eldegoss