Here is the full list of all 21 Elven Assassin achievements.
20K Fired Arrows
2.5K KilledOrcs
500 HeadShots
5K Fired Arrows
500 KilledOrcs
50 Head Shots
1K Fired Arrows
50 Orcs Killed
100 Fired Arrows
50 Window Shots
50K Fired Arrows
2.5K HeadShots
10K HeadShots
25K HeadShots
50K HeadShots
10K KilledOrcs
25K KilledOrcs
50K KilledOrcs
1K WindowShots
20K WindowShots
100 WindowShots