All the medals from gruntsrus.com

Killing Spree
Award: Kill 5 opponents in a row without dying
Availability: All gametypes

Killing Frenzy
Award: Kill 10 opponents in a row without dying
Availability: All gametypes

Running Riot
Award: Kill 15 opponents in a row without dying
Availability: All gametypes

Rampager
Award: Kill 20 opponents in a row without dying
Availability: All gametypes

Untouchable
Award: Kill 25 opponents in a row without dying
Availability: All gametypes

Invincible
Award: Kill 30 opponents in a row without dying
Availability: All gametypes

Perfection
Award: Win a slayer game with the score of 15 or more kills without dying
Availability: Slayer

Killjoy
Award: End opponents killing spree - any spree
Availability: All gametypes

Double Kill
Award: Kill 2 opponents within 4 seconds of each other
Availability: All gametypes

Triple Kill
Award: Kill 3 opponents within 4 seconds of the previous kill.
Availability: All gametypes

Overkill
Award: Kill 4 opponents within 4 seconds of each other
Availability: All gametypes

Killtacular
Award: Kill 5 opponents within 4 seconds of each other
Availability: All gametypes

Killtrocity
Award: Kill 6 opponents within 4 seconds of each other
Availability: All gametypes

Killimanjaro
Award: Kill 7 opponents within 4 seconds of each other
Availability: All gametypes

Killtastrophe
Award: Kill 8 opponents within 4 seconds of each other
Availability: All gametypes

Killapocalypse
Award: Kill 9 opponents within 4 seconds of each other
Availability: All gametypes

Killionare
Award: Kill 10 opponents within 4 seconds of each other
Availability: All gametypes

Extermination
Award: Get an overkill on an opposing team that results in all of the team being dead.
Availability: All gametypes

Sniper Kill
Award: Kill an opponent with the sniper rifle or beam rifle
Availability: Games with sniping weapons

Sniper Spree
Award: Kill 5 opponents in a row with a sniping weapon without dying
Availability: Games with sniping weapons

Award: Kill 10 opponents in a row with a sniping weapon without dying
Availability: Games with sniping weapons

Shotgun Spree
Award: Kill 5 opponents in a row with the shotgun without dying
Availability: Games with shotguns

Open Season
Award: Kill 10 opponents in a row with the shotgun without dying
Availability: Games with shotguns

Laser Kill
Award: Kill an opponent with the Spartan Laser
Availability: Games with Spartan Laser

Death from the Grave
Award: Kill an opponent after you have died
Availability: All gametypes

Splatter
Award: Hit and kill an opponent with a vehicle
Availability: Games with vehicles

Road Kill!
Award: Kill an enemy with a vehicle. Availability: Games with vehicles

Plasma Combo!
Award: Kill an enemy by blowing off a shield with the plasma pistol and then scoring a headshot.
Availability: Campaign

Super Detonation!
Award: Score a kill by filling an opponent with enough needles to cause a detonation.
Availability: Campaign

Multi Kill!
Award: Score 3 or more kills within 1.5 seconds to earn a multiplier for all of them.
Availability: Campaign

Headshot!
Award: Kill an enemy with a headshot.
Availability: Campaign

Steaktacular!
Award: Luke owes you a steak dinner. Availabiliy: All gametypes

Splatter Spree
Award: Splatter 5 opponents in a row with a vehicle without dying.
Availability: Games with vehicles

Vehicular Manslaughter
Award: Splatter 10 opponents in a row with a vehicle without dying.
Availability: Games with vehicles

Bonecracker
Award: Hit and kill an opponent with a melee attack
Availability: All games

Assassin
Award: Melee an opponent from behind
Availability: All games

Grenade Stick
Award: Kill an opponent by sticking him with a plasma or brute grenade
Availability: Games with plasma and brute grenades

Hijacker
Award: Steal an occupied vehicle from an opponent
Availability: All games with vehicles

Skyjacker!
Award: Board an aircraft
Availability: Games with Aircrafts

Wheelman
Award: Be the driver of a vehicle when a passenger kills an opponent.
Availability: Games with vehicles.

Flag Carrier Kill
Award: Kill an opponent carrying a flag in CTF
Availability: CTF Games

Bomb Carrier Kill
Award: Kill an opponent carrying the bomb
Availability: Assault games

Flag Kill
Award: Get a melee kill with the flag
Availability: CTF games with touch return enabled

Bomb Planted
Award: Plant a bomb in opponent's base
Availability: Assault games

Oddball Kill
Award: Get a melee kill when holding the oddball
Availability: Oddball games

Killed VIP
Award: Kill an opponent's VIP in a VIP game
Availability: VIP games

Hail to the King
Award: Kill 5 opponents in a row from inside the hill before it moves.
Availability: King of the Hill games

Bulltrue!
Award: Killed an opponent that was in the act of a sword lunge.

Killed Juggernaut!
Award: Kill the Juggernaut in a Juggernaut game

Juggernaut Spree!
Award: Kill 5 opponents in a row as the Juggernaut without dying.

Unstoppable!
Award: Kill 10 opponents in a row as the Juggernaut without dying.

Sword Spree!
Award: Kill 5 opponents in a row with the sword without dying.

Slice 'n Dice!
Award: Kill 10 opponents in a row with the sword without dying.

Incineration!
Award: Kill an opponent with a flame-based weapon.

Last Man Standing!
Award: Be the last human in an infection game.
Availability: Infection Gametype