I was thinking it would be neat to have something added to the game that would allow your character to do one superhuman feat per scenario. The move would come at a big cost but it would have the potential to alter the game in a crazy way. Of course this would have a risk to totally breaking the game...
What if Merisiel could do an assassin attack? Roll a D6, a 5 or 6 kills the enemy. A 1 makes her take 100% combat damage with no reductions. A 2, 3, 4 does nothing. No matter the outcome she can not move or explore her next turn.
What if Ezren could do an apocalypse attack? He calls a powerful spell that goes 5 cards deep into the location. Boon cards are immediately destroyed and bane cards are resolved (defeated or undefeated) but Ezren doesn't actually encounter them (no text goes into effect and he takes no damage). Ezren cannot cast a spell for the next 2 turns.
What if Kyra calls a phoenix? It brings back a character that has exhausted their draw pile and cant bring their hand up to the min. hand size. They recover half their discard pile randomly and place the cards in their draw pile. Kyra can no longer use her healing power the rest of this scenario.
hmmm....
It's an interesting idea in concept, but I do see a few major issues that would have to be overcome.
First, a major issue is that the game is balanced on several axes, and the size of the group will greatly alter the focus of that balance. For example, imagine Ezren's power in a solo game. Being able to effectively explore 5 times is substantially more powerful than losing the ability to case spells for two turns, since you rarely explore multiple times, so you effectively gained 4 extra turns at the cost of 3. In a larger game, though, where you count on everyone to explore 3 or more times, you're losing a lot more and very well may never use the power.
Second, I'm not a fan of once a scenario powers, because they tend to be hard to track. If you're doing this in a big group setting, and playing several games in a row, it can be easy to forget which scenario it was that you did the awesome rez to save someone, or that total dud assasination attempt. You'd need some way to track the ability, like burying cards or something like that. But at that point, why isn't the ability just a card?
Third, I'm just not sure what they add to the game. As I alluded to before, for big once-a-scenario effects, you already have cards with banish or bury effects. Now, these are obviously character specific, but then we get into space issues. These are large abilities that would take a lot of words to convey. There's just not enough room on the character cards for them.
Thinking about this, it seems like the only way it could work would be as a supplemental card, possibly a support card like a ship or runeforged weapons. That takes card of the space on the cards as well as the tracking issue. I'm not convinced that their cool factor would be enough to make up for the developmental nightmare it would be to use them. However, as I've thought about it more, I think it could work with enough effort. If you decide to go with this, I'm looking forward to seeing where it takes you.