Level 40 Pokemon Platinum....
Can't figure out how to defend against the blizzard!
Well........Crunch 1 Hit KOs Froslass. So Train Torterra up a bit more, and itll be fine. Theres also Yache Berries(sometimes found on wild Starlys) that weaken the power of Ice Type Moves.
Blizzard has low accuracy so one good idea is to hold Bright Powder to lower that even more. And use Crunch like Swampert said.
Or just switch to a better pokemon that could withstand an attack.