A temporary exile effect. Ignorant Bliss makes me think this could be red. In this case, the effect hits both players as an attempt to punish. As a single, random card, the effect is not likely to be useful (the dream is for combat tricks to be exiled this way]]]. This seems a very weak ability at uncommon, but I didn't feel red would get to target what to discard. I know that choosing to have the card say that spells couldn't be cast during combat a la Basandra, Battle Seraph would work for just wanting to hate on combat tricks, but my goal is to figure out what could be done with temporary discard.

How about a higher number of cards, so the chance to exile that combat trick at an inopportune time gets increased?

Is this a kind of randomness acceptable for Constructed?

Each player randomly choosing one card from their hand whenever this attacks can get irritating pretty fast in practice (as in throwing dice to choose the cards or so), but whatever; I don't think it's a huge issue.