They cannot be destroyed by any action in the game.
They can crush the entire icings in one go.
They can crush one layer of jelly.
They move every move.
Candies hit by them are not counted as an order.
They move after two moves.
They can be removed permanently by special candies.
When a toffee tornado lands on a tile where there is already a blocker, it can actually break that blocker or take a layer off, but also keep that blocker (if not totally destroyed) immune to other effects until it leaves.