Perish Song starts a countdown on each of the pokemon in play. The count starts at 3 when the move starts and is decremented at the end of each subsequent round. When it has reached 0, each pokemon that still had the count going will faint.
The count on an individual pokemon can be stopped by switching normally or fainting. If a pokemon switches out via Baton Pass, the incoming pokemon will inherit the Perish Song count.
Perish Song can not be stopped by any means. No moves or items can be used to prevent Perish Song from affecting both pokemon, including Detect/Protect. Nothing can pause the count and no move can prevent a pokemon from fainting when the count has run out.
Like all other non-damaging Normal-type attacks, Perish Song affects Ghost-type pokémon, despite their immunity to Normal attacks.
