Aside from those, how you take the deck is up to you, although wed obviously recommend using the other d20-based cards from Adventures in the Forgotten Realms
Jor Kadeen is also clear in their rulings that their desirable calculation is done once during ability resolution (hooray) "The value of X is determined only once, as the triggered ability resolves
Set up your monsters in an attack or defense position and start the battle phase
However, using coins and calling them "two-sided dice" isn't allowed
This high up, we'll go strictly by Whoever gets the most bans, wins. You can play Timetwister in Vintage (even if it's restricted) and Commander, but Yawgmoth's Bargain is strictly Vintage-only and one of Magic's best black enchantments ever
Ive just seen enough of this card in just 2022 to last me a lifetime