Fierits are very artistic especially with their kills, a special skill they have is to easily hide bodies by masking them so well with the background they look like statues, maybe even paintings. This trait helps them become stronger as it's insane and the most powerful they can do.

If the Fierite isn't violent they need to free themselves from the agony of not killing by making a blood-like substance from berries or whatever they can find and paint their frustrations away if failed to do so the Fierite can sleep kill. Fierits are destructive killing machines and without that being let out their bodies ultimately try to save themselves by killing somebody, it's obvious they have killed someone when they wake up with another face.

Every kill, every heart that stops beating, every family's tears just gets your stronger and stronger as they see you with their loved one's face. You're not okay, you're not normal you are a killer. You can do this for justice but that does not stop the voice in your head saying that you'll never truly have your own identity you'll forever be stuck with someone else's face until the next victim sometimes you think it's better that way and other times you think to yourself "who am I? Will, I ever know?" the answer is no of course not