You get 5 whammies. No more, no less. Normal sudoku rules apply, additionally:
If an empty tile is a knight's or king's move away from a numbered tile, it cannot have the same digit. Orthogonally adjacent tiles cannot have consecutive digits. (If there is a 4 in one tile, the tiles next to it cannot have a 3 or 5)
Orthogonally adjacent - Directly touching, the 4 tiles surrounding a tile.