Ramone Perseverance

Ramone's determination and willpower to stay alive and in control are so strong that once per a long rest. If he or Fafnir drops to zero HP, they instead drop to 1 HP. You then roll a d20 and gain HP back equal to the roll. After doing this, you must make a Constitution saving throw of 12 or higher; on a failure, you become unconscious for one round, gain one level of exhaustion, and switch control of your body to the other personality. On a success, you just gain the HP back, and the current personality stays in control.