first off beat the crap out of all the heavywieght champions.  
this will give you the secret characters:  DDP, Wrath, 
Glacier, and Randy Savage.
also a new league will open up, The World Wide Championship 
Wrestling!
If you manage to stay awake -and alive for that matter, 
(you need to beat 20 people!) You will face the almighty 
Joe Bruiser.
He is pretty easy to beat.

You will then have control over him as a playable character.
this boxer (yes I did say boxer) is extremely
powerful,unfortunatly he has no special move or grapple 
moves but just set the realism setting on and o' Joe wil 
beat everyone bloody, literally!
one of his biggest assets is what I like to call the 
"bruiser" just hold in the "A" and Joe will uppercut  
the hell outta anyone!