Yeah, it was fun spellbombing glint with my W/N. I used endure pain, had about 800 health, and did 800 dmg a pop with it. Yes, its max damage is your full health.
Note that if your target has less health than you, it will heal them and hurt you.
Did this skill get "nerfed" in the recent update? From discussion I've seen, it use to work when you had full health against a target that had a lot more health than you, effectively doing a crapload of damage. Now it seems like it only works when you are injured, and it will only do as much damage as 1/2 * your MAX-current health?
And Easy use of this skill is to use (W/N) Endure Pain, Then use Awaken the Blood, Blood Renewal, Balence. And you can do other chains to do the same thing.
But you'll gain lots more max health for a few seconds then drop down 50+% and do hundreds of dmg then be back @ full life in a few seconds. When Blood Renewal ends.
If I use this spell on them we will both be at 300, its points not percents. It makes you and the target at equal health. Can be good for a N/Mo spiker who uses Infuse Health and this, as far as I know this is the most damage you can do to some one with a single spell, but it can be risky being at low health.
It doesnt make your health's equal always. It does do that - except when grenth's cap is triggered. That is - you haven't lost much health, or the opponent has really high hp.
The interesting thing about Grenth's balance is it works both ways even though thats not mentioned in the skill desp. That means if you use this when you have more health then than the opponent - it works backwards and heals them and hurts you.