Scenario:
Wild double battle:
Opposing Flutter Mane uses perish song on Suicune and Terapagos.
Both opposing mons are knocked out and floor is cleared.
The next floor is a single battle, so Terapagos is automatically switched out and a single battle with Suicune and an opposing mon occurs.
Suicune's perish count persists, but if Terapagos is switched in, Terapagos' perish count also persists, despite it being switched out at the start of the battle.
Scenario: Wild double battle: Opposing Flutter Mane uses perish song on Suicune and Terapagos. Both opposing mons are knocked out and floor is cleared. The next floor is a single battle, so Terapagos is automatically switched out and a single battle with Suicune and an opposing mon occurs. Suicune's perish count persists, but if Terapagos is switched in, Terapagos' perish count also persists, despite it being switched out at the start of the battle.