With 2/2 in Pyroclasm in the Warlock destruction talent tree, it should invoke a 26% chance to stun targets for 3 sec using Soul Fire, Hellfire or Rain of Fire.
I’ve tested this, and something is clearly wrong. After 320 hits with hellfire, it only procced 1 single time. The pyroclasm procs seemed come more often with Rain of Fire for some reason… But still far from in 26% of the cases.
The stun chance is spread over the entire channel duration. So it’s not a 26% chance to stun per tick of hellfire but about 1.7% per tick. Rain of fire has fewer ticks so the stun chance per tick is higher.