During setup, you can optionally replace one Minion of Mordred card with Oberon.
The player who receives the Oberon card is evil, but his loyalty is invisible both to other evil players and to Merlin. This means that Oberon does not identify himself or herself as evil:
• when Merlin looks into the future during setup
• when the evil players open their eyes to identify each other during setup
• if interrogated by the Lady of the Lake (he reveals himself as good).