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Why not just make it so that everyone is countered immediately? Vampires up to level 4 could be made such that they are countered, as if they aren't quite fast enough yet to avoid being hit back. And while it's true that they should drain life, this value could be limited or, ultimately, the life-drain coefficient could be reduced; currently, it is 50% of the damage they deal. Here are the vampires by level:
1) 10%
2) 15%
3) 20%
4) 30%
5) 40%
6) 50%
7) 100%
Vampire shooters could be placed at levels 2 and 6, a Sorceress Vampire at level 5, and the rest would teleport or run. Some would attack with swords, some with teeth; daggers etc. could also be added.
So, what do you think of the idea?