EDIT: I updated the numbers in the post following the excellent comments by Vixsin and Lakh. I have very little background with this sort of thing, so the help is very appreciated! I hope no one read the post expecting revelations and great number gymnastics. I’m only a curious healer who tends to fixate on minor details and who doesn’t turn away from a challenge. I have no answers myself, but there are some great comments in the comment section for those looking for information.
Ever since I stumbled across a parse where I randomly did 5 million healing from Diffusion, I’ve been fixated on figuring out how that spell works.
Sadly, after hours and hours of pulling my hair out, I still don’t know.
In theory, Diffusion (available only on Heroic mode) is a debuff the Arcane Head puts on anyone who gets hit by its Arcany breath. The debuff redirects 10% of healing received to targets within 8 yards. It also stacks, which, if I understand right, would redirect 30% of healing received.
In practice, it is certainly a debuff put on Breath takers by the Arcane head that causes nearby players (and pets) to get healed, but how exactly it works is a still a mystery to me, even after I’ve gone nearly bald going through logs.
Anyone who, following this post, has further insight, is welcomed to share it. I’m happy to provide links to the actual logs if anyone wants to give it a go for themselves as well. Maybe I’ll finally get some closure and be able to move on with my WoW life.