The Perfection medal is a medal awarded in Halo 3 and Halo: Reach for winning any Slayer game with at least 15 kills, and without dying. It should be noted that you do not need to get a Running Riot medal, just 15 kills, which means the medal can still be obtained if the game selects a new host and resets your spree. If you are in a Team Slayer match, you have to get 15 kills by yourself without dying and your team still has to win.
It is represented by a black hexagon outlined in blue, with a smaller blue hexagon in the center.
One tactic to obtain the medal is to camp and avoid enemies. When they advance, stay out of sight, and as they get closer, execute an ambush or assassinate them. You can also try to perfect ranged attacks like sniping, or you can just play the game recklessly and hope you get 15 kills without dying. Camping and staying away from enemies can often result in a lack of kills, but you are more likely to stay alive for the whole game, so a mix between camping and advancing is good strategy. Perfection is considered one of the hardest medals to achieve. A recommended combination of weapons is the sniper and the shotgun on both Halo 3 and Halo: Reach as this combination allows you to cover all levels of ranges.
In Halo 4 expert vehicle users can get perfections with more ease than a Spartan on foot. An example of this would be using a Banshee with great skill, and having a very good driver in a Warthog. It is possible to also get a perfection in a Ghost, but since this vehicle doesn't have much health to last an entire game, especially with concentrated enemy fire, it may become necessary to replace the damaged Ghost and resume. in addition, it helps greatly to have the Operator's Wheelman Tactical Package, as it gives vehicles more health and resistance to EMP blasts, as well as the Explosives Support Upgrade, which combined can allow a Warthog to be hit by a Scorpion's shell and survive.