Although he has not thrown an MLB pitch in 2015, Jake Arrieta threw 9,529 pitches that were tracked by the PITCHf/x system between 2008 and 2014, all of them occuring in the MLB Regular Season. In 2014, he relied primarily on his Slider (90mph) and Sinker (94mph), also mixing in a Fourseam Fastball (95mph), Curve (80mph) and Change (88mph).
Basic description of 2014 pitches compared to other RHP:
His slider is thrown extremely hard, results in many more groundballs compared to other pitchers' sliders and has less than expected depth. His sinker has well above average velo, has less armside run than typical, has little sinking action compared to a true sinker and results in somewhat more groundballs compared to other pitchers' sinkers. His fourseam fastball is a real worm killer that generates an extreme number of groundballs compared to other pitchers' fourseamers and has slightly above average velo. His curve has an exceptional bite, generates a high number of swings & misses compared to other pitchers' curves, is slightly harder than usual and results in somewhat more groundballs compared to other pitchers' curves. His change is much firmer than usual and has slight armside fade.