Elite Backstab

Those who have mastered the attack of backstab can 
further increase their effectiveness of their attack. 
Elite backstab enhances the backstab skill such that each
time it is used, it deals additonal damage equivalent 
1 to 5 times the user's DEXTERITY.  This also affects
circle damage.

The classes that get the skill elite backstab are:

assassin   : Level 105 (excellent)