I'm sure. There is a Mega-Dragon in the World of Xeen (MM4 + MM5), somewhere in the clouds. Now that I think about it, I seem to recall he had 25,000 hitpoints and you got 100,000,000 experience points for killing him. But experience was different back then.Just a quick googling turns up this video of killing the Mega-Dragon: http://www.youtube.com/watch?v=h6W3FO63R-U
Turns out he was worth 232 gems
He probably is the all-time #2 M&M baddie. He didn't have regeneration of course, like the MM9 Dragon King does.