Below is a fun puzzle from Mark's Magic: The Puzzling book.
I Once Cast a Fireball THIS Big
"It's your draw step, and you pick up a Fireball. You only need to do 12 points of damage to win, but that seems irrelevant right now. The real question is: How big of a Fireball are you capable of making? Check your best answer against ours tomorrow to see how you've done."
Each card image is clickable to view a larger image and the current Oracle wording.