Castle Panic can even be played as a solo game by just one player. All the standard rules apply to the solitaire version with the exception that the player draws up to a hand of 6 cards.
Also, during the Discard and Draw phase, the player may Discard up to 2 cards at once (instead of just 1), and then Draw 2 cards to replace those.
There is no Trade Cards phase, as there is no one to trade with. Be prepared for a challenging game.