Andy Ruiz Jr warned Anthony Joshua not to be fooled by his physical appearance when they collide in New York on June 1.
Ruiz has stepped in to face the WBA 'Super', IBF and WBO champion at Madison Square Garden, live on Sky Box Office, after Jarrell Miller failed a drugs test.
Joshua is seeking a 'spectacular knockout' to stay on course for a mega fight against Deontay Wilder or Tyson Fury but Ruiz believes his confrontational style can wreck the Londoner's US debut.
"I'm an aggressive fighter that throws a lot of combinations," he said. "I'm not scared of getting hit. I love action fights.
"I know a lot of people underestimate me just because of how I look, because of my body, but that has nothing to do with me fighting.
"Yes Anthony Joshua is buffed, he has a lot of muscles, but you don't need a lot of muscles to learn how to fight, to take punches and be strong.
"I've proved that a lot of times. I've fought a lot of big, muscular guys but that doesn't really mean anything.
"As long as I let my hands go, throw the combinations and stick to the game plan, we are going to win this fight.
"Joshua hasn't ever fought somebody like me. I don't think he knows how to box and move back.
"He hasn't fought anyone who matches my speed and the pressure I'm going to bring."
The bout with Joshua presents Ruiz with the chance to write the wrongs of his first world title fight in 2016, when he suffered a controversial points loss to then-WBO champion Joseph Parker.
It remains his only professional defeat in 33 fights.
"Joshua is a great champion and has fought a lot of good fighters including Joseph Parker, but in my heart and eyes he has a belt that belongs to me, that I won against Parker when we eliminated each other in New Zealand.
"It is my opportunity to make history and become the first Mexican heavyweight champion of the world, and to claim what's mine - the WBO title.
"It motivates me a lot. It's my second opportunity. I'm still young and have never been hurt or knocked down in my professional career.
"This means a lot to me and it couldn't have happened in a better way. I've just had a fight [he stopped Alexander Dimitrenko on April 20] and gone back into a training camp.
"My condition and preparedness is going to show on June 1."
Watch Anthony Joshua against Andy Ruiz Jr and Katie Taylor's undisputed world lightweight title fight versus Delfine Persoon at Madison Square Garden in New York on June 1, live on Sky Sports Box Office.