Doesn't playing 1 character for that long start to get boring? I have to mix it up to keep it fun
Not even slightly.
Who was the lucky character to get 999?
Sly for me.
Playstation All-Stars Battle Royale Accomplishments:
1st Ever rank 999 (only for full game, not beta)
1st Ever Double Black Belt In 1st 2 seasons (2v2 and Free For All)
1st Ever Black Belt (Acquired in Free For All)
1st Ever 2v2 Player to 300, 400, 500-1300 wins
1st Ever 2v2 Player to Black Belt level 300
1st Ever Free For All Player to Black Belt level 100
2nd Ever 2v2 Black Belt
Finishing the trials will get you to level 56. Then playing free for all battles can get you anywhere up to and possibly more than 20 levels no matter how high of a level you're on. This isn't like RPG experience systems or FPS experience systems where you need a lot more experience each new level. It seems on this game that every level requires the same amount of experience.
I main Parappa and got 999, but I've played quite a bit with Sir Dan, Toro, and Dante.