His build is a high risk build which requires a lot of mobility and stealth. His condition cleansing comes from Jaunt (remove one condition per jaunt), also, I would assume he's using renewing oasis a trait which helps mitigate conditions by reducing condition duration and provides him regeneration every time he using mirage cloak. Only flaw with with the use of this trait is that if a "good condition" thief was stacking a ton of poison he would have something to worry about as this trait doesn't affect poison but with the use of jaunt this is hardship that can be over come.