This achievement is pretty self explanatory; beat every battle scenario in arcade missions on both light side and dark side, which seems to be the solo ones, not co-op. It doesn't have to be 3 stars, just the 1 star completion should count.
Happy hunting!
Edit: It seems this achievement progress bugs for some people so make sure you keep an eye on the achievement tracker for this one! I didn't have this happen to me but if you completed them all and sit at 93%, try doing another random mission or a 2 star mission.