S4 Bonechill stages have the biome effect:
Cleanses all status ailments at the end of the turn for 5 turns. But there’s a way to temporarily circumvent that.
If you leave one monster alive before entering the boss stage and wait until the biome effect refreshes, and kill the monster on the next move, or alternatively with an item, you have 4 turns of the boss stages not cleansing anything, until the biome effect refreshes again.
Just noticed this earlier and didn’t see it shared anywhere yet. Might be useful to some, especially for finishing hard mode stages.