The Mark of Evil is an ominous image that has appeared in fire and in Paintings of the Past, and the Cobra's Venoms. It is in the shape of Scar's left eye. It appears where the source of fire Scar appeared through burned.
According to the Paintings of the Past, the Mark of Evil is a symbol associated with evil lions of the Pride Lands' past. The very first Lion Guard, led by Askari, created a powerful force to halt the evil lions, using this symbol as their marking.
According to the story told by Scar in "Battle for the Pride Lands", the Mark of Evil appears to refer to a very specific type of scar, one caused by a cobra bite which causes bad thoughts and great pain and anger to the victim unless cured however the effects do vary. Tuliza plants are capable of easing the effects, but only for a short time. Should the lion or lioness want to be healed, they must journey to the Tree of Life and go through several rituals and/or tasks for long periods of time before they are finally healed.
When Kion spots Janja, he catches a glimpse of Scar's fiery ghost just before it vanishes, causing him to say "What in the Pride Lands?". After the hyenas and the jackals are defeated, Kion goes to the area where Scar appeared and sees that a scorch mark with a strange symbol remains. Rafiki recognizes it from the Paintings of the Past as a sign of terrible evil and goes off to consult the Paintings of the Past for further information.
After Bunga thinks that Kion has turned evil because of his scar he runs away from his friends. Kion looks at his reflection and sees Scar in it. Scar says that he has the Mark of Evil just like him. Kion says that he may look like Scar but he'll never act like Scar.