All Stars’ -2 Power Min 1 is one of the most powerful clan bonuses, in my opinion. It really nerfs a lot of cards including Montana and Uppers. Their natural enemy is, of course, Piranhas/Nightmare (SOB).
Similarly, the Bangers’ and Ulu Watu’s Power +2 bonus is also very effective. This power does better the more pills you use but it can be useful in low pill fights as well. It’s also a nice intimidation factor. When some players see a power 8+ card, they may just throw in the towel or toss a damage reducer rather than trying to beat the card. This can allow some well-timed furies to get through.