Description for despair mastery: Debuffs applied to enemies reduce their healing and Regeneration effects by X% each.
With Despair 3/3 each debuff reduces healing by 15%.
At 6 debuffs, you get 15 x 6% = 90% healing reduction. 7 debuffs, 105% and 8 debuffs, 120%.
As seen in this video, despair is not reversing the regen after 7 stacks of debuffs.
https://www.youtube.com/watch?v=Rw-M4meda14
There's no reason why despair should not be able to reverse regen when there are champions with petrify abilities that are capable of reversing regen. Please look into fixing this.