You might want to limit it by targeting lowest rarity first. The situation where this discards a rare and cripples the opponent's stock would be too damaging outside a Brigand deck.
Speaking of using this against something that isn't actually a Brigand deck, I would hate to see this come up against my Undead deck if I summoned
Hungry dead into my hand via keyword (It's not otherwise in my deck...) and lose 24/24/24. I just don't see any way to prevent it happening, and there's probably no way to recover losing so many gems and recruits as Undead. Maybe it should only take effect if there are three or more Brigands in the opponent's hand? But I don't want to make the card useless, either. 3x cost is just terrifying in some cases.