I have played around with this idea for an mlp comic for some time. This would be a minor character. He is the pony who first brought death to the MLPverse. He gained his cutie mark while putting an injured animal out of it's misery. His parents panicked and killed him, hence the permanent wound to his chest. He spends the afterlife guiding the dead to to his domain(s).
Hard to see with this picture, but he is a colt, I would say a bit older than the cmc.

Again, concept idea for a minor character, might change, who knows