Leech Seed launches a seed towards the enemy. If successful, the seed
"takes root". On each subsequent round, the enemy's HP will be decreased
by approximately 1/16th of its maximum value, and that amount of HP will
be transfered to your Pokémon (if your Pokémon is not at max HP). Note
that the HP leeched from the enemy will be transfered to whichever of your
Pokémon is currently deployed: it needn't be the one that first used Leech
Once the seed is planted, it can be removed through the use of Haze, or by switching the seeded Pokémon
Leech Seed is ineffectual against Grass Pokémon.
Using Leech Seed in combination with Toxic
yields an interesting (and extremely potent) side effect. See the Toxic
page for more detailed information.