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How long does it last? Perish Song kills off any Pokemon who was on the field 3 turns ago that hasn't switched out. Its also unaffected by Magic Bounce. :0
Maximum 3 turns. If any of the Pokemon who were in battle stay in for all 3 turns, they faint. If a Pokemon switches out, Perish Song wears off on that Pokemon.
If a Pokemon has Soundproof, then they won't be affected by Perish Song.