There are other ways to kill Dopelganger particularly the Awaken the Blood skill + sacrifice spell. But these is a new way just in case you do not have the ATB spell. im not sure if there are similar post, im too lazy to search, but if there are... my sincere apologies to the authors.
i already tried these build 3 times succesfully. heres how it works.
you basically need 3 spells. but your main spell damage will be backfire.
Distribute your skill points to
1. Domination = max
2. Curses = leftover
Skills You need
1. backfire
2. Emphaty
3. Spiteful spirit
Just fill the other skill slots that are fast cast (pref with less than 1 sec cast time) with useless kill preferably those that are offensive spells(i chose offensive blood attributes)
Strategy
1. approach doppelganger close enough to malee range.
2. cast Backfire first then Emphaty then spiteful spirit. Your goal is to make self inflicting damage to him while he is under the Backfire spell.
The Emphaty and Spitefull Spirit are just in case that he attacks with malee you also deals damage to him.
With 12 Domination, Backfire will be dealing 119 damage per spell cast. If you chose spells that are cast less than 1 sec, you will deal damage faster than you can say bruguduybrugudungstungstuy.
With 11 curses, you will be dealing 50+ damage just in case he attempts to attack you with malee.
It will only take Dopelganger to cast 4 spells to kill himself.
I did not even bother attacking him with malee. Poor sucker killed himself.
Good luck.
P

Then yes, if you continue to work backwards sure, use spiteful spirit, or better yet why don't you use Aura of the Lich instead?