Also: Consider the variant to rock-paper-scissors in which "fire" may be thrown once in your lifetime. How do you really adjudicate/enforce that fairly?
A couple of examples from early classic Lee-Kirby Thor issues (maybe not the most perfect of case-studies, but what I have at hand here):
- Journey Into Mystery #85 -- Thor's first clash with Loki (encompassing the whole issue) ends with Thor dunking him in the East River. "According to legend, Loki's magic powers are useless in water!" he says. Obviously, that was never effective again.
- JIM #93 -- Thor's first battle with the Radioactive Man. Among the unexpected one-off things that happen here are that (a) Radioactive Man would "blow up like an H-bomb" if subjected to any physical violence, and (b) the issue ends with Thor summoning a tornado in New York that can blow the Radioactive Man all the way back to China, where he then mushroom-cloud explodes as predicted.
- JIM #114-115 -- The Absorbing Man is another good example of a seemingly unstoppable foe who is basically never beaten the same way twice. His first dramatic appearance ends with Thor "spinning my enchanted hammer at cyclotronic speed, [so that] I have the power to transmute the elements themselves!"; after which a bystander says "It was like a nuclear explosion! Even the ground is glazed!". Thus Thor has created helium gas, forced the Absorbing Man to change into it, and floated him into space. This will never happen again.
- Thor #171 -- Here, a long battle with the Wrecker ends with Thor throwing him onto the powered third-rail of the New York subway system, and then connecting Mjolnir to it to drain away all of the Wrecker's supernatural strength (allegedly de-powering him "fore'er"). I'm particularly uncertain how you'd ever deal with circumstantial power-changes or de-powering of different characters (pretty common in the comics) in the game setting.