My group has been having some very bad encounters with the overlord ever since scourge was introduced (I do not think heroes have won a quest since).

Is scourge broken or is it more of a problem with mists and chains that rust?

It seems like the perfect card: 1 xp for a pretty much guaranteed 1 extra monster (but usually more). And it's strong too! Hits like a truck sometimes with that red die

The scourge can hit hard, but it's only melee. The fatigue ability can be tricky, but heroes generally can play around it. The soulbinder class is indeed a powerful OL tool, and Mists/Chains are campaigns which don't pull any punches for the heroes. Using the soulbinder during a Mists/Chains campaign will demand a lot of the heroes, for sure. I don't think I'd call it broken, for the most part.

the Raven flock is by far more broken ; you can oftenly spawn it almost anywhere, sometimes having a bonus reinforcement, and since it can move to 4 spaces, it can activates many overlord objectives and grants many actions. The biggest issue from my game experience from many years