Using the seal of power tranformed the zant from a fearsome demon into a puppy, even on hard difficulty. he didnt made enough damage on my 2 warriors to use a potion. However, I still didnt managed to beat his regen on hard. Prolly need more levels or farming, which I dont want to make at the moment.

Therefore, if you plan to finish the game on difficult, this is the one seal to use to make your life easy.

Cheers.