Raises the foe's PP usage.
Pressure is an ability that makes the opponent use 2 PP instead of 1 for each move they use against the Pokémon with this ability. In longer battles, this can be very useful as it can deplete the opponent's PP more quickly, potentially causing them to run out of usable moves. A Pokémon that is spamming Recover or Hyper Beam will find itself in a tough spot against a Pokémon with Pressure.
It's also only found on legendary Pokémon as a primary ability.