I'm currently working on a novel adaptation of my comic, though it isn't up yet ^w^"
Shilo is immortal, but with a catch. The collar around his neck is enchanted. So long as he's wearing it, no matter how grave the injury may seem, he cannot die. He does not have any special self-healing or regeneration powers though, so say for example, if he had a limb cut off in battle, he'd have to have it surgically (or magically) reattached.
Once you remove his collar, he's just as mortal as anyone else. The trouble lies in reaching the collar, seeing as how it located underneath a set of very, very sharp teeth and behind four paws worth razor-like claws.