Yes, you can use any deck in a Direct Challenge match. This is one of the things that makes Direct Challenge so fun and flexible. Whether you want to test out a new deck, practice with an old favorite, or try something completely different, you're free to do so in Direct Challenge. However, keep in mind that the deck you choose can significantly influence the outcome of the match. So, it's a good idea to choose a deck that aligns with your strategy and playstyle.