In an unusual move, Blizzard has spelled out exactly how the proc on Val'anyr, Hammer of the Ancient Kings works. There are probably one or two of you who consider it a spoiler, so I'll put it after the cut.
- There is a 10% chance whenever healing is done by one of your HoTs or direct heals for you to gain a buff called Blessing of Ancient Kings for 15 seconds. This has a 45 second internal cooldown. Heals that are entirely overheal – such as HoTs ticking on a full-health target – do not have a chance to proc the Blessing.
- The Blessing causes all of your heals (for the 15 seconds that the buff is up) to put a shield on anyone you heal absorbing 15% of the amount healed for 8 seconds.
- This shield stacks with itself, will proc from HoT ticks that occur after you gain the Blessing, and includes overhealing - if I have the Blessing up and hit someone with a 13k Greater Heal, of which 10k is overhealing, they get a shield for (13k * 0.15) = 1950 damage.
- There is a cap of 20,000 on the shield effect.
If all of this is confusing you, go check out the examples on Bornakk's post, which are very helpful.
Now I want this even more. It's too bad I have no interest in 25-man raiding.