One of my players did a wonderful thing by explaining what one of his characters (Doctor Strange) was planning on doing about Elderstahl and it's status. This immediately made me think of a set of milestones for this powerset, which could be used for any powerset that has a dangerous downside and isn't native to the character.
This Terrible Burden
1 XP When you discuss the negative ramifications of unleashing the powers of your dangerous powerset.
3 XP When you are defeated in a scene where you refuse to use the dangerous powerset, even when it would clearly have helped you.
10 XP When you either find a way to safely remove your burden and place it somewhere where it can do no harm to anyone, or when you decide that you are far more powerful and wise than you previously thought, and you claim the right to utilize your terrible new powers, regardless of the consequences.