As the self-appointed defender of the burn yourself down Fanatic I approve of this power. It still is a 1-1 for Martyr, but 8 damage as a single shot is no joke, that burns a lot of DR granting minions in one shot. Not too shabby.
I would think that unlike GL PWFanatic would be using her base power sparingly, and be dealing most of her damage with her other cards, but it has some decent uses, and if it is off a sheet of paper in a folder it isn't written in stone.
I would absolutely love it if you took damage and then healed a bit back though, that promo woul be an instant favorite for me.
You could take out Citizen Truth completely with just your power phase, or Runes of Malediction (which is awesome since that gives the rest of the team time to get rid of Effigy.
Beat down significantly on any of the higher health really nasty cards, like EPE or Voss' ships, or the Paradoja Magnifica, or La Capitan's crew.
My point, a 5 for 5 damage exchange is very situational, since 5 damage is replicated well by other heroes, but 8 for 8 is a huge chunk of damage that as of right now could swing games and save a lot of HP vs. the 8 you lose.
Situational yes, hurts a lot, yes, but it would also be really powerful.
Then there would be the interplay between GL and Adept and PWFanatic. Take three send the power Adepts way who does what he can before sending it to GL who sends it back to Fanatic, healing her 1 and letting her Martyr.
Or even just taking three to let Tempest use rain, esp. if you have embolden on yourself. deal yourself 2 radiant, then play a card, deal yourself three radiant, everyone heals 2, then Martyr with 5 damage already stored.
This Fanatic would play more selfishly and risk death more, and that isn't a popular playstyle for her, but it is effective, much more so if this promo happens.