Now, I don't know about you guys but I think Scar can be considered Mentally Ill. One of the main reason Scar became evil due to the venom of the the Strange Cobra's venom. That is very comparable to many versions of the joker who became way worse than they were before because of being in contact with laughing chemicals. The most comparable is Jeremiah Valeska. Both were just normal beings, until they came in contact with a toxic substance that change the victims personality to the worst (the snake venom and the laughing gas). Due to being so similar, he can count.