I once soloed (how the hell do you spell that ??!###!)
an assasin/mage
Its a nice combo:
Do NOT use him as a fighter though, you cant buff him up with protection spells and then kill evrybody with a sword ...
You'll have to rely on the mage for most of the time
The poison-extra is nice, though it gets less usefull once savingthrows of enemy's go up, still the concept of being an assasin is just FUN
anywayz, it's more than possible to do