Medusa is definitely possible. I haven't tried it solo, but I've fought her 4-5 times in small parties and never had to take a step away from her as a sampire. Died a few times on the first visit, but on the last three visits only time I got close to death was when I was surprised by an undead gargoyle when turned to stone.
Standard sampire template, not fully trained, as follows:
Skill current/target
Bushido 115/120
Swords 120/120
Parry 95/120
Tactics 100/100
Necro 100/100
Anatomy 100/100
Chivalry 75/60
Slasher of Veils I'm not sure. Only fought him once at it wasn't on my sampire. I think it would be an extremely tough fight though. Stygian dragon would be a negative as far as I can tell. Fought him 3 times and had many many deaths each time. The way he moves, how hard he hits, what that does to stamina and speed, and how difficult it is to hit him for big damage are all difficult things for a sampire to overcome. Much better done with archers and mages I think.