Seeing Brock Lesnar staring you down across the octagon is an intimidating enough proposition. But even though Frank Mir is the only man who has been able to best Lesnar in his mixed martial arts career, he is expecting an even greater challenge in tonight's rematch for the Ultimate Fighting Championship heavyweight title.

"I'm prepared for the worst Brock Lesnar anybody could imagine," Mir said during a recent conference call. "I have to (be)."

The rematch, which headlines the UFC 100 card from Las Vegas, is available on pay-per-view. It's a unification bout of sorts, as Lesnar holds the heavyweight title, while Mir has an interim version of the title.

It's hard to imagine a Brock Lesnar scarier than the one who knocked out the legendary Randy Couture to win the championship last November, or a scarier Brock Lesnar than the one who pummeled Heath Herring for 15 minutes last year.

But Mir has seen how rapidly the former Bismarck State wrestling champion has taken to mixed martial arts, and he figures he'd better be ready for Lesnar to take another quantum leap.

"We just went ahead and prepared for the worst-case scenario that Brock knows everything I know about mixed martial arts," Mir said. "And on top of that he's stronger and bigger and faster than I am."

Lesnar has established himself as a force in MMA, dominating all four of his fights. Even in his loss to Mir, Lesnar controlled about 80 of the 90 seconds before getting caught in a kneebar by Mir, a jiu jitsu expert.

Lesnar's wrestling skills - he won an NCAA championship at Minnesota to go with the NJCAA title he captured at BSC - were a given. But he has also showed incredible striking power. Lesnar knocked Mir, Herring and Couture off their feet with punches, and forced his first MMA opponent , Min Soo Kim, to submit to strikes.

"Well, I think (it's) just having the ability to evolve," Lesnar said. "I could have been very pig-headed when I made this transition from a pro wrestler to an ultimate fighter and said, 'Well, I'm just going to use my wrestling technique and my strength and speed.' That would have been very ignorant of me to do so.

"The ability for me to have an open mind and an open game plan, you know to keep my eyes and ears open and my mouth shut and acquire the right people around me to train me."

Mir added that Lesnar's reach - 81 inches - has been a critical reason his standup has been so effective.

"I remember even watching (Couture), when he slipped that punch from Brock, he thought he was out of the way," Mir said. "And that punch kept on coming and it kept on coming and it kept on coming, and finally it just - it hit him and it caught him and he went down."

Mir said that he's brought in training partners who are 6-foot-7 or 6-8 to simulate Lesnar's reach.

In their first bout, Lesnar swarmed Mir and seemed close to stopping him with hammerfists before a controversial ruling by referee Steve Mazzagatti resulted in a standup and point deduction from Lesnar. Mir admitted Lesnar's size and speed were tough to handle.

"That's one thing that I really took from my first fight that I made sure I trained for for this fight was there was times when I was on the ground that I lost him," Mir said. "I was like, 'He's on my right side. He's punching me … where'd he go? He's on my left side. And I had to watch the tape to actually see what happened and watch him rotate from one side of my hips to the other."

But the all-out attack Lesnar employed in his first three fights was nowhere to be seen against Couture. Instead Lesnar was more patient and systematic in his approach, which impressed Mir.

"They're hard to watch tape on, because you don't know how much more he's going to improve every fight," Mir said. ".. . From Heath to Randy, you see him very composed, standing in front. I remember my trainers were sort of like, 'Hey man, is he just standing there and actually fighting strike for strike instead of just bull rushing across the cage?' … That only took one fight to fix that. So it makes it a little difficult on my part to actually sit there and assess what we're going to prepare for."

Lesnar said he works hard with his trainers to ensure he keeps evolving.

"You spend so many hours with these guys, you'd really have to be an idiot not to pick up on anything," Lesnar said. "And so I guess my key factor is my willingness to learn, and I'm very coachable."

That's why Mir dismisses the idea that the fight will come down to his submissions against Lesnar's wrestling as an oversimplification.

"It's kind of funny, because that's such a real simple way of looking at it," he said. "… If I go to the athletic club down the street, the gym, I'd be hard-pressed to find many guys in the gym that are stronger than I am, and I guarantee that Brock is not that unknowledgeable about jiu jitsu or in grappling, I mean he spends every day training in the art of MMA."

And Lesnar is eager to apply what he is learned in his first title defense - and to avenge his only loss.

"We've spent a lot of time in the gym, a lot of time watching film - a lot of blood, a lot of sweat, a lot of tears," Lesnar said. "… This training camp was a very hard, very hard training camp. That's the hardest part, I'm just looking forward to the fight because that's - to me getting in there and actually doing exactly what you love to do is an honor and a privilege."