I know that one of my biggest challenges as a player is using expendable resources. I always, always, always
feel like I might need them more later. And usually I'm right, which doesn't help.
The intended "flow" for TorgE seems to be: You start with a few Possibilities. You use a couple. Needing more, you up the excitement with a card, replenishing your Possibilities at a cost. You spend a few more Possibilities. Someone ups the drama again. Then you reach the final scene -- which will generally start with the enemies having an advantage while the PCs build their card pool and trade cards to set up, before finally blowing out their cards and Possibilities and winning the day. Everybody goes home laughing and talking about The Awesome Thing I Did.
Once an Act ends and a new Act starts... the new Act usually builds up along that same flow, so they start slow, and you have time to rebuild.
I don't know. Speaking as someone who plays a lot more than GMs, I really do see both sides on this, which is tricksy. I can see how I'd be disappointed if I ended an Act with 7 Possibilities - having, very likely, put the whole group in danger a few times with my Cosm Cards to get those - and suddenly they don't matter.
On the other hand... I can't think of a better answer, frankly. Roll them over to the next Act? Now I'm worried that if I don't do that, I'm going to regret it next session. Convert them to XP? Now you're back to using Possibilities to advance, and that's something US fixed for a very good reason. Convert them into almost any other kind of reward? ...Same thing, really. Possibilities need to be their own reward.
I considered working it from the other side (and I bet they did, too) -- say, you can never have more than 6 Possibilities at a time, so once you have 6, anything that would earn you more is wasted. But people needing to earn more Possibilities is critical. Nobody's going to play a card that triggers a Dinosaur Attack if they don't need more Possibilities. Keeping yourself maxed-out would proof you against things like the Law of Decay; you could cheerfully lose a shoelace, since you're not going to gain anything anyway.
*Maybe* you could offer something different for the Possibility-granting cards in the final Scene of an Act. Say, they could take Possibilities if they want them, or
they can boost the XP reward for the Act a little bit by making the final Scene more difficult. I'm not sure, though - that greys the line on not using Possibilities for XP and I don't know how it would work.
... Really, the way Acts are designed, that should be
the right time to reset everything, but if it's not, that's easy to do - enough that that's really my best thought on this, despite my usual insistence that yes, House Rules work, but only if you're the GM.
Curiously, the way things are set up, I don't see people playing cards to make an encounter more difficult "because it's too easy". I see them doing it because they're almost out of Possibilities, which probably means things already aren't going their way. Which is an interesting dynamic. I don't know.
I think that should be code for any deserving player. "I could happily have dropped a ravagon on them!"
Oops! Clumsy me, always dropping my ravagons. Good thing they're not fragile!