Foiled is a great card, which can be explained fairly briefly:
Numerics
- Recap: Often times 1 resource = 1 threat mitigated.
- Costs: This card has a 0 printed cost, the card itself is an inherit 1 cost. Total cost = 1.
- Threat mitigated: 1 to 3 threat possible. Obviously you're not playing this card when the boost is 0 and there's no cards with 4 boost icons... yet.
- In summary: This card is a 1 cost and can mitigate 1 to 3 threat.
Conclusion
If 1 resource = 1 threat mitigated; this card has the potential of being 1 resource = 3 threat mitigated. Which is great! However, I suspect it will usually be 2 threat mitigated since a minority cards have 3 boost icons.
Is the card worth playing to mitigate 1 threat? That's situational on how much you need that resource in the given moment. It plays like Emergency at that point.
There is a critical weakness to the card, which I often suffer from with Preemptive Strike, which is being in the right form when you draw this card. In solo play, this card requires you're in either Alter-Ego form or being hit with a scheme trigger like Advance. In multiplayer, your options open up a lot.
I think this card is worth considering in a lot of Justice decks. It's a 0-cost, which makes it very approachable for low hand-size heroes like Thor (ew) or She-Hulk (less ew). I think it's solid for Iron Man since you can use it while in Tony Stark form without hampering your resources (and it's an energy resource for Repulsor Blast). Unfortunately, multiple Foileds don't stack, so Ms. Marvel doesn't really benefit all that much from the card. I also think Justice already has A LOT of ways to mitigate Threat and those ways will often compete in slot with this card (for instance, I don't run this in my Black-Widow since she already has threat locked down with preparations).