Recently I was playing ninja-mages deck. After I gained 14 points my deck run out of cards. What should I do when I can't draw cards anymore? (because my deck is empty)
This is covered on page 4 of the rules.
If you need to draw or reveal a card and your deck is empty, shuffle your discard pile. Put it on the table face down—that’s your new deck. Start drawing from there.
If you have no discard pile as well, that would be a very odd game! I've never seen a game go anywhere near that situation though.