halo hopper, 16 all american barrel, handle(extender), custom aimer.
barrel, electronic hopper if you can shoot fast enough to need it, maybe a flatline trigger
Easy to get parts,
Stock barrel, stock hopper, no handle, skips if you dont have an electric hopper.
It is a good working gun, even without upgrades, but it would work so much better if you got a better barrel for it. I like the gun. I use it in all my games now instead of the tippman. I have customized mine so it shoots a little bit harder by adding an extra spring and that helped me a lot. the only downfall is it is a little bit louder.
Buy it for cheap, use it a lot, if u dont like it sell it.