I'm a new player, after winning the second battle of Sparky's challenge, I didn't get the reward for that battle, and the Sparky's challange event completely disappeared, both from the main screen and the Events tab (Play->Events), and Sparky commented that now I'm ready for the Starter Deck Duel. I'm really disappointed, because I wanted to try out all 3 event decks and get all the event rewards.