Whirlpool lasts for 4-5 (extra) turns after its used – at least, this is how its supposed to function
in Pixelmon, then turn Whirlpool is used counts as 1
why is this important? well, the only function of whirlpool really is to whirlpool trap
with this different whirlpool mechanic, when you usually would be able to whirlpool+perish song to guarantee a kill (as long as you survive the turns), they can be freed from whirlpool on the final turn of perish song