Believe it or not, I did not know that a character named Mr. Dream was the final boxer you fight in Punchout.  Fights just like Mike Tyson, so I beat him on my 1st try, but I only found out he existed when I put the code in I normally use to fight Iron Mike on MTPO.   I actually laughed out loud when I realized I've been playing Nintendo for almost 30 years, and did not know this!

Yeah, I didn't know the codes where interchangeable either-- had to find out the same way you did. lol

I've only played MTPO and never regular Punchout on NES, and didn't know that until now.