What is the trigger mechanic for the wizard passive critical mass?

Question

This question is no longer relevant as the skill has been removed from the game as of Patch 2.0.1

Critical Mass is a wizard passive: Critical Hits have a chance to reduce the cooldown of your spells by 1 second.

Do you know what is meant by "chance" ? It is probably something like an increasing chance over time that decrease every time it triggers, because if it was a flat % chance it would be in the description.

Most wizards cooldowns are about 15 seconds. When compared to evocation (reduces all cooldowns by 15%), critical mass needs to trigger at least 3 times every 15 seconds to be better than evocation. In my current setup, this is never the case. I would say that I deal about 10 critical hits in a normal 15 seconds fight. It is most of the time 1, sometimes 2. So I would guess that the base probability is something like 10%. My critical chance when doing this was 7%, so I think you have to increase it by a lot in order for critical mass to be effective.

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Update: Critical mass recently got patched:

Fixed an issue with certain powers that had a higher than intended chance to trigger Critical Mass

It is still not clear how it works. Apparently it depends in what skill you are using. The only way to be sure is actually testing in the game what the skill does; and I find it very frustrating. I want to be able to design a build without having to test myself every spell independently, or searching though the web if someone did it.

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Update (1.0.3): With the attack speed nerf, critical mass got un-nerfed. There is a build called windup based on the fact that energy twister with wicked wind makes critical mass trigger very often.

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Update (1.0.4): Now the skill energy twister - wicked wind used in the windup build has his modifier reduced by half, so the build is still good, but not as good as it used to be.

Answer 1

For the Critical Mass passive, what is meant by the "chance" is that it is determined by the proc coefficient of the spell you cast. Single target spells have 100% "chance" to reduce the cooldown by 1 second while AOE spells have differing sets of proc coefficents by spell AND rune. There's a few sites that break down proc coefficents of various spells which applies to crit chance as well as return on LOH. Here, and here. Luckily people with more patience than me seem to have most spells crit proc chance figured out.

Some useful proc chances for popular wizard spells:

Hydra: 0%, Hydras never proc
Magic Missile / Seeker: 100%
Shock Pulse / Piercing Orb: 25% per target hit
Blizzard / Snowbound: 2% per tick per target hit
Energy Twister / Wicked Wind: 10% per tick per target 
Explosive Blast / Chain Reaction: 11% per target hit per explosive (of 3)

I've recently been trying the Windup Wizard/CM build which still seems pretty effective, and a bit silly (in fact it was the easiest way for me to beat inferno Ghom). From personal experience I've found that on my wizard, when I run over 40% crit chance while using a build like windup wizard, everything is off cooldown pretty much all the time.

Answer 2

It is a straight percentage chance for each critical hit.

Currently, there is a build that exploits this with the help of gear that raises the chance for critical hits as well as gear that provides extra arcane power for critical hits. If you use Living Lightning or Wicked Wind, chances are you won't be able to mash the buttons fast enough to use up your arcane power and cooldowns.

Answer 3

Source: http://eu.battle.net/d3/en/forum/topic/5208511084

Critical massCritical mass has a probability to trigger out of a critical equal to the proc ratio of the skill used to score that critical. In clear if CC is your critical hit chance and R is the ratio of the skill used you have : CC.R per monster hit chance to trigger CM out of using that skill or if you prefer : R per monster hit chance to trigger CM out of scoring a critical with that skill Concerning dot with very short time between each damage : it appears that the game keep the random value used to pass the ratio check for each damage dealt by the dot. That mean that each damage has only to pass a critical check. This lead to an absurd amount of CM trigger on dot if you are lucky enough to pass the proc check.

First the critical hit chance is constant no matter what your skill use

If your critical hit chance is 50% then every tick, every attack, will have 50% chance to crit. It has some damage advantage.

However, what we're really interested are things like life per second, or critical mass.

So, after you crit someone, the probability that the critical mass build will crit is not guaranteed. Some attack that tend to hit many enemies have lower rate proc.

For example, if you use Arcane Mines skill.

Say you hit 100 times

50 times of the time, your attack will crit 50%*50%*100=25 times you will proc critical mass.

The truth is arcane mine rarely hit only one enemy. So things sort of balance off.