Medals

There are eight medals you can get when playing, four of them when playing on the Casual or Regular difficulties, and four when playing Expert or Nightmare.
The first four are Bronze, Silver, Gold, and Platinum, while the second four are Sapphire, Emerald, Ruby, and Diamond.
You collect Bronze and Sapphire if you have one remaining core when the match ends. If you have two cores, you get Silver or Emerald. Three cores gets you Gold or Ruby. If you manage to complete without taking any damage to the cores (shields don't count) you'll get Platinum or Diamond.
== Operation Alley ==
This map is unlocked by default, and as such, does not require anything to unlock.
Medal 	Item 1 	Item 2
Bronze 	None 	None
Silver 	Skin "Red Menace" 	Weapon "Red Menace"
Gold 	Buildable "Glue Trap"	None
Platinum	Head "Tactical" 	None
Sapphire	None 	None
Emerald 	Military Prefix Pack 	None
Ruby 	Head "Commando" 	None
Diamond 	Unknown 	Unknown