Change your preferences here.
Deals damage and has a 10% chance to lower target's Defense one stage.
Acid is, like most low-power moves, completely useless competitively. If you want to lower the opponent's Defense, Screech is easily better. For a more powerful Poison-type move, Sludge is much more powerful. Don't bother using it, ever.
Leer deals no damage but lowers Defense by one stage 100% of the time.
Screech deals no damage but lowers Defense by two stages 100% of the time.