A few possible bugs (some may already be reported):
Dread Mist Spell costs 30mp instead of 10mp
Dread mist seems to miss sometimes. Using it in the wilderness, sometimes (maybe on slopes) it caused no damage.
Dark Ascendant Bite - not seeming to kill. With the regular Dhampir, I got the skull icon sometimes. So far I have not been able to kill a cowered enemy and gotten the skull (though I have killed some - but likely due to outright damage). It could just be the DC is to low and I have been unlucky with the monster save rolls.
Biting Swarm - damage is not 1d12. I am seeing damage that is low (or bad luck) even for 1d6.
Vampiric Blast appears to be healing or 1d3/level, not a flat 1d3. Please keep!
Observations:
Other than the bugs, it is a lot of fun to play. The healing while blasting is fun. Can't say much about the Growing Dread feature. I did not have any luck noticing I was getting stacks of Growing Dread on monsters. They were dying to fast, and when I did use the finishing spells, the initial damage was always enough to kill. So if the Growing Dread feature is working as intended, and the damage is only 1 dice of damage per growing dread, it might be worth it to make them a little easier to build up - making the mist bigger, making the mist start a condition that lasts 20-30 seconds that causes you to acquire Growing Dread, or making it 2 Growing Dread per eldritch blast might make it more effective - or I might just not be doing it right...
Suggestion:
Enervating Blast in TS looks like such a perfect complement to the Bargainer. Any chance it could also work with Vampiric Blast? If not, how about making the Empty T4 for both Bargainer and base Dhampir - "Whenever you would drain a level from a target, you drain double the number of levels." It would help to make up for the lost healing, and it would make level drain items and spells a lot more dangerous (situationally) in the hands of dhampir. If double is too much in some instances (high level bite, Energy Drain), even just making the ability add +1 level drain would add some benefit in some situations.