Pressure is an ability that was introduced in Generation III that doubles the foes PP usage for every successful hit. It still works if the Pokemon is immune to the move used (such as Acid being used on a Steel-type). Outside of battle, if a Pokémon with Pressure is at the front the party, it decreases the chances of battling a higher level Pokémon by 50%.
Twenty Pokémon have this ability, thirteen of which are legendary.
In Generation IV, it says that "<name> is exerting its Pressure!"
Pokémon who have this Ability
Single Ability
144 Articuno
145 Zapdos
146 Moltres
150 Mewtwo
234 Raikou
244 Entei
245 Suicune
249 Lugia
250 Ho-Oh
461 Weavile
356 Dusclops
477 Dusknoir
386 Deoxys
416 Vespiquen
442 Spiritomb
483 Dialga
484 Palkia
Dual Ability
142 Aerodactyl Rock Head
359 Absol Super Luck