Above the main reels you will see an additional reel, premium symbols can land either partially or fully in view on this reel. When any symbol lands in view, it will turn all examples of it on the main reel set into wilds. If more than one of the same symbol appears fully, a multiplier will be added to the wild. All wins will then be reconsidered with the new wild symbols.
Occasionally, a nudge symbol may appear on the fifth reel, if it does, any partially visible symbols on the Tophit reel will move fully into position, potentially creating new wilds or multipliers.