Hey this is my ever post on this site
1. Get to a training dummy
2. Turn all your frost runes and blood runes into death runes, by either using festering Strike, icy touch or blood boil.
3. Wait for all of them to regenerate.
4. Now spam icy touch (using your blood runes with icy touch.)
5. Now your unholy runes magically turn into death runes, though your blood runes were used.
I'm not sure if this is intended in the game but I read the spells and the passives and nothing suggests that it should.
What happens is that your blood death runes suddenly force your unholy runes to become death runes, though your blood runes go on cooldown and turn back to being blood.
I use the trick a lot to build up my burst - the only problem is waiting. But once your blood runes fall back off cd, and use you use 2 blood boils you will be sitting on 6 death runes.
With blood tap and soul leech that's another 4, so a total of 10 necrotic strikes and with strength procs that is 10x 70k health absorb which will 700k+.
I'll be making a video about it soon on my youtube because I know it can be hard to understand.
In the meantime please check my channel out for more content like this
https://www.youtube.com/user/TheChaz112