Showdown in the Savage Lands
Step 1: one character challenges another to a duel. It doesn’t have to be a formal challenge, but an understanding between the two that somethings going down.
Step 2: both characters accept and lay out conditions, if any, for the duel.
Step 3: An opposed Intimidate check or Deception vs Insight. Both can happen at the same time if one is going for intimidation and the other deception. The loser has disadvantage on its attack. Winner has advantage and if they succeed it is a critical hit.
Step 3: Roll Initiative if both are still standing.