[Circle Orboros] Cassius and Wurmwood...any good?

I've been looking at the dynamic duo, and I really cannot see how to use this warlock effectively. Cassius' fury is meh, he has no support spells for his army (either infantry or warbeasts apart from the ARM debuff), he has literal deadweight in the form of Wurmwood which cannot move on its own and has DEF 5, and his offensive spells are either expensive (Hellmouth) or underpowered (Stranglehold). Not to mention the very underwhelming feat. Also he has no place in 15 pt lists at all.

The only possible interesting thing about the feat I can see is that when you disable a model with Tough and it succeeds its Tough roll, it gets knocked down with 1 life, but the feat then deals 1 damage again to the model for being knocked down, which disables it AGAIN and then Tough kicks in again. The cycle repeats until the model fails its Tough roll, which is eventually, then it stays dead. So the feat effectively nullifies Tough.

Is there some synergy I'm missing here? Is there a minion out there who suddenly makes them awesome?

Not yet. As of the moment, it seems he works well with wolds and some of the tharns. (Those with treewalking). I see him as being effective only in armies of 35 points and above, since then you have more options.

He's painful to play against legion, since they can see through forest, so you're screwed over.

Ceh. Maybe I can use druids to poke models in its command radius and hope for a critical knockdown, just to deal the free 1 damage.