Sorry everyone, kinda got busy and didn't get a chance to make threads. I should be able to put stuff up on the weekend, maybe tomorrow.
Generally, if you challenge someone to a duel and they accept, one person puts the element they're summoning in a spoiler block, then the other one summons an element without looking at the spoiler. The two elements are compared, whoever lost rolls on the table for the element the winner used, and that's what happens to them. Hopefully, no one decides to cheat by looking at what their opponent summoned before picking their own element. (If it's an issue, players can PM element choices to someone - myself, or if I'm in the duel, another player - and we'll go on with that. It's a little slower, though.)