If Ariados' "Leech Life" attack does 30 damage but the opponent's Active Pokemon has only 10 HP remaining, how many damage counters will be removed from Ariados?

Leech Life does 30 damage, which is not affected by the fact that the KO only required 10 damage. Therefore, Ariados will remove 3 damage counters, or all if there are less than 3.

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