My recommendation would be cards such as Kain [13-073H]
Each starter deck includes everything you will need to play right out of the box
The resulting spell's color, mana cost, mana value, and so on are determined by only those alternative characteristics
Demonic Pact is our best "gift." We can play it, keep it for three turns to use all of its good modes, and then give it to our opponent on the turn before we'd have to choose "Lose the game," leaving them with only one super-painful choice
When you next cast a creature spell this turn, that creature enters with two additional +1/+1 counters on it
Some stores may have a competitive crowd and might handle prizes differently, while others stick to the Lorcana League format, keeping things relaxed