Here are all the medals.

Medal Awards How to get it

Gunslinger-Precision Pistol-6 Kills with Pistol

Frenzy-Elite Assault Rifle-12 Kills with Blaster Rifle

Demolition- Guidable Rockets-4 Critical Hits vs. Vehicles

Technician-Vehicle Regen-Slice into a Vehicle

Marksman-Particle Beam Rifle-6 Headshots with Sniper Rifle

Regulator-Flechette Shotgun-8 Kills with Shotgun

Endurance-Energy Recuperation-8 Points

Guardian-Shielding-16 Points

War Hero-Damage Increase-24 Points