!if (character in "Priests Shadow") /castsequence reset=60 Mind Blast,Mind Blast,Mind Blast,Shadowfiend,Dispersion,Mind Blast,Mind Blast,Mind Blast,Mind Blast,Mind Blast,Mind,Blast,Shadowfiend,Mind Blast,Mind Blast,Mind Blast
Another comma instead of space.

Was thinking, Mind Blast is 8 seconds cooldown, talented it becomes every 6.5 seconds.
Dispersion has a 2 minute cooldown.
Shadowfiend has a 5 minute (4 minutes, talented) cooldown, and 5 seconds is knocked off of the cooldown for every Mindflay critical hit.

We have 14 casts, after Dispersion before Dispersion is called again.
Since a Mindblast cannot cast, until 6.5 seconds after the last...
We have 15 x 6.5 = 97.5 seconds until it could fire off.
However, this is the proc macro, which should average a click every other press, long term.
With approximately 15 GCD's from the first macro, we won't often have Dispersion stick.

Shadowfiend will likely stick.
Six casts of Mind Blast is 39 seconds, minimum.
Plus the duration of Dispersion, 6 seconds.
That's 45 seconds, plus roughly 7 spells from the first macro.
I'd think it would stick at that point.