Despite the fact that the stats page will list 9 pro challenges there are actually 10 required to get the achievement (and 11 total in the game).
once you've got 80% of all the goals completed on the pro difficulty or better you'll get a message from Tony Hawk to meet him in the Slums for a pro Challenge.
This is also the goal that bumps you up to #4 in the top 8.
As for beat a developer, just play on online a few times. Maybe I'm lucky but I got it my first game... you do actually have to win though.