Need a group of people to get this done, as this is the last achievment/quest I need to get done for my Warlord of Draenor title. This will also grant you the Achievment The Last of Us, and Lord/Lady of War title.
You will need Gladiator Sanctum level 3 in your Garrison. I have multiple characters that can help the people that help me even after I have won the game. Winning a arena match results in the quest marker (100 slain in the arena) to be auto completed. You can not que up for the Arena again until weekly reset after you win, that is why I got more characters to help the other people in the group after I have gotten what I wanted.
Add DoctorPete#21107 if you want to do this achievment.