Against staggered enemies, your crit range with rogue attacks expands by 2.

Adventurer Feat: 

You gain a +2 attack bonus against staggered enemies.

Champion Feat: 

Your crit range against staggered enemies expands by 2 (now +4).

Epic Feat: 

Whenever a staggered enemy misses you with a melee attack, it's vulnerable to your attacks for the rest of the battle.