The Shadow Ghoul

The hideous creature that "killed" Rufus Schwarzkreuz when he was human and turned him into the first ever Shadow Stalker. The Shadow Ghoul is a gruesome monster of unbelievable physical strength and resistance. Most weapons can't hurt it. Bullets don't even put a scratch on it's armored skin and most energetic forces just get neutralised by it. The creature's claws and fangs are poisonous, even a little scratch kills every known lifeform. Why Rufus wasn't killed but somehow absorbed it is still unknown to the day. However, it is known that the Shadow Ghoul is capable of killing the Shadow Stalker. Due to the poison of the creature, the wounds it cuts Rufus won't heal and he would suffer and die from them like an ordinary human being.
In other words, the Shadow Ghoul's blood and poison are Rufus' kryptonite.
This doesn't do the Corporation any good cause Shadow Ghoul blood is not exactly easily to get. It is unknown how many of these creatures exist and what it's exact origin is. Some people think that this beast is a mutation created out of the infamous Blaze implosion that wiped-out Gagonda. But proof to this will only be found if this creature can ever be studied.
Well, good luck!

The Shadow Ghoul belongs to me!