A new option for 5e Oriental Adventures. The rules are taken from 3e OA with little modification (which is was taken from 1e OA with little development work as well – none really needed). They work fine almost as is 5e.
Far less lethal than an iaijutsu duel, a psychic duel involves two samurai staring each other down—focusing their energy until one decides to yield to a superior opponent. Such a duel usually occurs under much less formal circumstances than an iaijutsu duel — for example, when a noble samurai forces a teahouse bully to recognize his superiority and skulk away.
Like an iaijutsu duel, a psychic duel is strictly a one-on-one confrontation. Only intelligent humanoids, monstrous humanoids, and giants can participate in a psychic duel. The participants cannot have crossed swords already during the encounter, and they cannot duel in the middle of a raging battle. If either character is attacked during the psychic duel, the duel ends with no victor.
To resolve a psychic duel, the characters spend a full round facing each other, within 10 feet of each other. Each character then rolls an Honour save against DC 10. If one character succeeds and the other does not, the successful character has won the duel. If both characters fail the saving throw, the duel is inconclusive and neither wins. If both characters succeed, they are locked in the mental battle and the duel continues for another round, with the DC rising to 15. The DC rises by 5 each round the duel continues. Should one character break off the duel and attack before it is resolved, he is the loser.
The loser of a psychic duel has two options. He may either retreat or attack, but if he attacks he has disadvantage on all attacks, saving throws and ability checks against his victorious opponent for the duration of the encounter. If he retreats, he must avoid the winner of the duel for at least one day or suffer the same effect.