This achievement is unmissable and is for completing Mission 6, no surprises there. However, this was the first boss that gave me a bit of difficulty so I thought I would include a couple of pointers here.
I'm sure there are numerous builds that would beat this guy effectively but here's what I did:
Weapons: Spin (for the boss), Grip (for the mobs)
Spin Mods: +Recharge while shielded, +Damage to armor
Grip Mods: +Damage after Kills, +damage for headshots
Personal Mods: Launch efficiency, Health Recovery
I hadn't had a need to use shield much prior to this guy, but his launch ability does massive damage, repeatedly bringing me to a sliver of health if I missed a dodge or was distracted by mobs.
So I would launch at him multiple times bringing his shield down as far as I could, then unload with Spin to clean up any remaining armor and chip away at his health. When Spin was spent, or if I got hit by one of his projectiles, I would pop shield and run around the map picking up health shards. (CAUTION: Mobs will melee through shield, so be sure not to let them get too close.) Then release shield at him or a nearby mob, rinse and repeat. For mobs, a couple of headshots with Grip put the first one down quickly and the mods allowed me to then make short work of any others nearby before again focusing on the boss.
Hope this helps, if not, please leave feedback in the comments for what I could add.