Evasion Bonus is a support ability available originally only to Thieves. Thieves received this bonus starting at level 10. While it is not represented in a character's statistics, it is generally accepted that the bonus is +10 Evasion. This Evasion bonus increases for Thieves at 30 to +20, at 50 to +30, and at 70 to +40.
Since the expansion, Treasures of Aht Urhgan, Puppetmaster and Blue Mage also get Evasion Bonus, though to a lesser extent than thieves. Puppetmasters gain a +10 bonus at level 20. Blue Mages may gain +10 bonus at 69 through blue magic synergy.
Dancers from the expansion pack Wings of the Goddess also gain Evasion bonus.