Leech Seed plants a seed on the target that drains 1⁄8 of its maximum HP at the end of each turn and restores it to the user, or any Pokémon that takes its place. It does not work on Grass-type Pokémon; it does technically work against Pokémon with the Magic Guard ability, but no HP will be sapped.
It always drains 1⁄8 of the opponent's maximum HP and restores it to the user (or it's ally), so it is a typeless damage.
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