...by constructing a deck with only one creature or artifact in it, then picking dice until you get a "You get [a random creature or artifact from your deck] in the next duel!".

One obvious way to fix this is to, instead of having a 50% chance of getting either life or the free-card-in-next-duel when case 1 is chosen in sub_443940() (at a cursory glance, whether to give you a quiz or a freebie is chosen when the dice is generated), instead pick a random card from your deck; if it's a non-aura permanent, get that for free; and if not, get life instead.

You'd still be able to make a deck with all "You win if you get this into play" permanents, but it would take a lot more effort, and you wouldn't be able to include lands either.