Mad Priests on Madmortem

Ok, while looking up how inscription might perform as a raiding profession (seems rather swell currently) I ran over the following glyph:

Glyph of Spirit of Redemption – All heals cast while Spirit of Redemption is active have a 20% chance to increase the remaining duration of Spirit of Redemption by 20 sec.

Do not understand me wrong, I expect this to either get nerfed or already have been nerfed / removed from the game, etc. by the time you are reading this.

However, let us just assume this glyph makes it into the game… What do you think about the following tactic:

“Ok, Priest runs in, dies, then Boss X gets MDed by our pretty hunter to the MT…”

There is a very simple assumption in this: After the first time (you only got 15 sec) you simply need to cast an expected 5 casts per 20 seconds to keep the spirit up forever. Since the spirit never runs OOM or dies in an AE, quite an interesting idea, huh?

However, these kind of statistics can have a problem: The thing simply might not want to procc… So, assuming no special cooldown or anything like it, let us simply calculate the chance that we are going down casting flash heals.

Currently a flash heal takes Dionadar 1.27 seconds (haste ftw!) – this is not totally overblown, since there would be no need to look at mana efficiency.

During the first 15 seconds, I will therefore be able to get 11.81 casts on the go. However, due to lag/etc I will only assume 10 casts. Since each cast has a 1 – 0.2 = 0.8 chance to not procc the gem, there is a 1 – 0.8^10 = 0.8926 (almost 90%) chance that the 20 seconds will proc. (If the 11th cast also gets squeezed out, the chance would be 91.41%, so this does not even make a big difference)

Now, the chance that somebody makes a stupid mistake ruining everything is surely a lot higher on a progression night than 10%, so this is pretty acceptable!

If you managed to take that initial 15 second hurdle, there is always at least 20 seconds time left to get the next procc of. (Funny enough, you can expect a lot higher time, since it says “increases duration”, so if it proccs 3 times in a row right in the beginning, you already got the buff to more than a whole minute…) The amount of flash heals – or CoHs – you could get of with the speed up that currently is about 281 haste, is now 15.75:

Chance to procc another 20 seconds with
14 casts: 95.60%
15 casts: 96.48%

Soooo, in conclusion: The chance that you will be able to keep this up for almost 10 minutes is at least:
slow casting variant: 0.8926 * 0.9560 ^ 29 = 24.22%
fast casting variant: 0.9141 * 0.9648 ^ 29 = 32.35%

Since we can assume you brought at least one warlock or one druid and since the GCD is pushed down to 1.27 seconds as well – There is a pretty damn good chance you will keep spamming the new and shiny intelligent CoH on 6 targets through the whole damn fight!!