After completing Blizzard Island, you'll find the entrance to Crevice Cave.
On this dungeon, there are 10 floors then a checkpoint. There is then 4 more floors, and then the 5th is the boss room.
You'll mostly find Ice Types and Water Types.
I recommend bringing 2 Fire Types or moves, and two Electric Types or moves to prevent them from dieing from the Water Types.
Pokemon You May Find
That isn't all of them but that gives you a good idea of what type of Pokemon you'll be facing.
On the last floor, you'll face Froslass. Just use Fire Types against her Ice-Ghost Type Combination. They'll do quite a bit of damage and will eventually knock her out.
When defeated, you'll find Scizor, frozen. He'll thaw out and will give you the "Secret Rank" back in Treasure Town.