I think Fedor has a shot at beating him as does Big Nog. Maybe Mir could do it again, but not so sure. Maybe Barnett. Other than that can any MMA fighter in any weight class beat him?
Very good question and I also like your assessment.
Though I think Fedor would actually beat Lesnar easily.
Here's a shocker: I think Rashad Evans(!) would be a very bad match up for Lesnar.
I know Evans is in light heavy now, but he would IMO have no problem controlling Lesnar and get a decision.
BTW, I think Evans is boring as hell.
As for heavy weights:
Noguiera will probably win. I don't see Lesnar winning that fight. Lesnar can't knock out Noguiera, nobody can. And he won't be able to submit him.
And Noguiera has more gas in the tank to take it to Brock beyond round 2.
Mir... I love Mir.
Mir is a tough matchup for Lesnar. He can't go to the ground with Mir, Mir is that good with the leg locks. The Lesnar fight rejuvenated him. But I still think Lesnar can overpower Mir. The right strategy would be to push Mir up against the fence and pound on him.
Bottom line - I think those who will have a chance at beating Lesnar are fighters who have a dimension that Lesnar lacks. Eg, advanced ground game or very good conditioning.
Because no matter how hard Lesnar works his conditioning - 280 lbs of muscle won't be dancing in the 4th and 5th round.