Most of my cards disappeared. They're still in my deck, but they won't show up when I battle something, only the 6 cards I get from my wand and 1 card I get from a necklace. I have 2 decks at the moment, and I have cards in both of them. Why won't they show up?
Sounds like you don't have a deck equipped young Wizard. Just like a hat, you must equip your deck in order for it to work!
Go to your backpack and click on the deck tab - select the deck you want to use and double click it. The way to know that a deck is equipped is to look for the closed hand icon to the left of the name of the deck.