Miro would be a cross between Vader and Bane.
He comes back unannounced and maims a lower level guy. Pops up on dark and takes out a couple more. Shows up on random shows just beating the hell out of people and saying nothing. Speculation starts to abound about what he wants and people start demanding answers in response to the amount of guys he has taken out.
Finally after a month he is advertised to speak on Dynamite and explain his actions. He details that he who was once God's favorite champion has now been forsaken and he will leave a trail of bodies in his wake as sacrifices until his standing is restored. This megamanical rant is interrupted by some midcareer, doesnt matter who cause they're gonna be food, let's say Brian Pillman. "You've been attacking people from behind, putting people on the shelf, including my friend. Why dont you fight me man to man?"
Match happens: Miro crush. Back on the mic, he firmly declares that people will keep getting hurt until he gets his shot at the title and the chance to restore his previous glory. TNT champ comes out to accept the challenge, but Miro flatly tells them, hes not interested this time he has is sights on the World title.
More bodies are broken until Cowboy has to answer the call. Depending on how over both are at that point you could give Miro the belt (Vader), but irregardless the end result should definitely be Cowboy being broken physically (Bane). Let's go with keeping the belt on Cowboy as Miro destroys him, the ref, and anybody else who steps in his way as the match is thrown out.
Cowboy still champion, but physically and mentally broken, must now summon the courage to get back up and face the physical embodiment of his fear, a man who is now crowing about being God's favorite (uncrowned) champion. You can debut Lana around this time as Miro will be less singular minded and to introduce a weakness to be exploited in the rematch.