Thanks ^^
To the top left of the board is a number called the stock, it shows how many blocks have yet to fall into the board. Once it's down to 0, no more blocks will fall. Reshuffling while there are still blocks on the board will cause cursed blocks to appear, so I recommend emtying it as much as possible before refilling.
Nightmare is tough for sure, I recommend ranking up if possible, and getting a heal combo spell. Getting one of the pyramid relics could also help a lot!