Leech Seed plants a seed on the target. After a target under the effect of Leech Seed takes its turn, 1/16 of its HP will be drained (rounded down, but not less than 1), and the same amount of HP will be restored to the target's opponent (even if it was not the Pokémon that originally used the attack). Recurrent Leech Seed draining will not occur if the seeded Pokémon defeats the target. Unlike other types of damage, the recurrent damage done by Leech Seed can exceed the target's current HP. Leech Seed will not work against Grass-type Pokémon, and attempts to seed an already-seeded Pokémon will fail.
Leech Seed draining will occur even if the seeded Pokémon knocks itself out with crash damage, recoil damage, or self-inflicted confusion damage, or by making a substitute before the end of its turn. Draining from Leech Seed is done after continuing partial trapping damage and recurrent poison or burn damage. Leech Seed can be removed by Haze or switching. If the target is seeded during a round that it switches in, it will take recurrent damage during that round, but only if its speed is less than or equal to the user's speed.
If the target of Leech Seed is also under the effect of Toxic (or was under that effect and healed itself with Rest), because Leech Seed and Toxic both use the same damage algorithm, Leech Seed damage will be affected by Toxic's N parameter, and will increase each turn.
⅛ of the target's HP is drained instead. Rapid Spin will release a Pokémon from the effects of Leech Seed. Also, Leech Seed no longer interacts with Toxic damage and Haze no longer affects Leech Seed. If a Pokémon uses Baton Pass, Leech Seed will still be under effect, even if the switched in Pokémon is a Grass-type. The user can no longer plant a seed on a target with a substitute (but setting up a substitute does not release a Pokémon from existing effects of Leech Seed).
Generation III onward
Leech Seed will now drain HP at the end of each turn.
In battles involving multiple Pokémon, Leech Seed will only heal the Pokémon that is in the same position as the Pokémon that originally used Leech Seed was in. If no Pokémon is in that position (for example, if it fainted and could not be replaced), Leech Seed will not take any health from the seeded Pokémon. However, if a Pokémon is later able to occupy that position (if it was revived), Leech Seed will once again sap HP from the seeded Pokémon. While a Pokémon is seeded, even if it cannot have its health drained due to there being no Pokémon in the appropriate slot to drain its HP, it cannot be affected by Leech Seed again.
Leech Seed can be used as part of a Pokémon Contest combination, with the user gaining an extra two appeal points if Growth was used in the prior turn. It is also part of a Contest Spectacular combination, with the user gaining an extra three appeal points if Rototiller was used in the prior turn.
If the target has the AbilityLiquid Ooze, the user takes damage instead of restoring HP. If the user is under the effect of Heal Block, Leech Seed will not restore any of the user's HP. However, the effect damage will be dealt normally. If the user has a Big Root as its held item, it will recover 30% more HP than it normally would. Big Root does not increase damage dealt. All other effects remain the same.
If powered up by a Grassium Z into Z-Leech Seed, all of the user's lowered stats are reset.
In Super Smash Bros. Melee, Leech Seed is one of the random outcomes of Togepi's Metronome. All characters within the area of effect will receive a flower on their head that causes 5% damage every few seconds.
A seed sprouts from Bulbasaur's bulb, which shoots out to the opponent. When hit, the opponent becomes wrapped in thin vines and leaves that restrain it. The vines and leaves then glow red and suck energy from the opponent. Sometimes, the vines have no leaves at all.
Skiploom shoots one or two seeds from the middle of the flower on top of its head towards the opponent. When hit, the opponent is wrapped in vines that restrain it. The vines then glow red and suck energy from the opponent.
Shroomish shoots multiple seeds from the hole on its head towards the opponent. When the opponent is hit, the seeds sprout vines which wrap around the opponent. The vines glow red and suck energy from the opponent.
Pumpkaboo shoots several seeds from its mouth into the ground. The seeds immediately grow into vines that latch onto a target and drain them of their energy. When a Grass-type Pokémon is seeded, the target is still bound by the roots, but they are a dull gray-brown color, and it is unaffected by the energy draining.
Gogoat fires multiple seeds at the opponent. The seeds immediately grow into vines that bind the opponent, or Gogoat fires a seed from its mouth into the ground. The seed immediately grows into vines that latch onto a target and drain them of their energy.
Gourgeist shoots several seeds from its mouth into the ground. The seeds immediately grow into vines that latch onto a target and drain them of their energy. When a Grass-type Pokémon is seeded, the target is still bound by the roots, but they are a dull gray-brown color, and it is unaffected by the energy draining.
Jumpluff holds its arms above its head and releases a stream of cotton from the cotton puffs on its head and arms at the opponent. The cotton sticks to the opponent and sprout vines that ties up the opponent.
Sceptile touches the opponent with the tip of its tail, releasing a seed from it and planting it onto the opponent. The seed then sprouts into vines that wrap around the opponent's body and absorbs its energy, or a vine with leaves on it sprouts from one of the seeds on Sceptile's back and wraps themselves around the opponent, draining its energy.
Projétil de Semente (XY082)* Semente de Morte (Diamond & Pearl-Secret Wonders) Semente Sanguessuga (XY087-present, Unleashed-present, manga, The Official Pokémon Handbook) Sanguessuga (The Official Pokémon Handbook) Chupa-Vidas (The Official Pokémon Handbook)