Seen on Android and on Plarium Play. Playing Doom Tower using Mithrala and Khoronar (Void Only Hard Secret Room as an example). I use them together in Doom Tower, sometimes with and sometimes without Minaya on the team.

When an enemy has a Hex on them and attacks Khoronar, and Mithrala's Petrify activates and petrifies the enemy, Khoronar often will not counterattack (definitely not 100% but certainly often enough to notice). 

Ferocious Guard (Passive)
Counterattacks when hit by enemies under [Decrease ATK], [Decrease DEF], or [Decrease SPD] debuffs. Always counterattacks when hit if Minaya is on the same team. 

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The attached photo shows that all of the enemy champs have Decrease Attack and have Decrease Defense. In this photo, both Krisk and Wurlim (I think) attacked Khoronar and were Petrified, and Khoronar did NOT counterattack either time. After this screenshot was taken, St Nicholas attacked Khoronar and the counterattack happened.

Please have a look. Thank you for your time, consideration, and hard work!