A typical starting opening for us is to Mhegeddon into Vampiress into Sanguine Hunter, with Demonic Link on Vampiress. Put the 2 damage either on yourself or Vampiress, depending on the game state. Sanguines and Vampiress are probably your best units. Get the Eye out as soon as you can, you'll need the mana.
Don't bring out Mhegeddon vs the Beastmaster, though. He'll just summon a bunch of asps, boost them with Badger Frenzy, and turn Mhgeddon into a teddy bear. And if you don't bring him out first turn, you might as well not bring him out at all. You'll have to take a different route for that (the Demon that can toss weaken tokens would be a good choice if facing Asps).
Siphon Life is good to damage/kill anything with a built in Def, since they can't defend against it, and armor doesn't protect from it. I'd take out a Crumble (if you're running them) for 1 Curse Item; I hate using full actions to take out something that was cast as a quick.
Theft of Life can be useful on Ehren to try to slow down the healing, but it's really good against the BM's Regen Belt. Curse of Decay is usually too slow by itself, needs to be supplemented with something, maybe burns. I'll edit the post when I think of more tips.