Tonight we were playing through our first game and a question with might came up. I was in a situation where I was able to spend all but one of my prowess. I had one might in my hand. Could I have not used the might and simply discarded it or does it need to be put back on the stack? I argued that since I wasn't spending it I should be able to keep it but was ultimately over ruled. Was I right or was the rest of the group?
You were right. You're required to draw your bonus card for Might, but you're not required to play Might just because you have it. This is why the Cleanup step requires you discard the cards you played and the cards left in your hand.
Might can also be useful against the Glacien, because discarding it isn't the same as spending it, so Might is often a good thing to discard to their "discard a card" effects.