Here is the full list of all 13 Unnamed Fiasco achievements worth 1,000 gamerscore.
Achieve 100% in the single player challenges.
Keep the flag for two straight minutes in Capture the Flag mode.
All players have died in a short period of time (in 4-player mode).
Win a Dog Tag game with least kills.
Perform 3 Triple Kills in a single match.
Be the player with fewer points at sometime and still win the game (in 3 or 4-player mode).
Win by scoring more points than all other players combined (in 3 or 4-player mode).
Do not get killed in a Police Chase game.
Kill at least one player every time you are the police in a Police Chase game.
Retrieve 5 Treasures in a row in Treasure Hunt mode.
Get most of your kills when the Minute Madness is enabled.
Get five kills without using your gun.
Be the first one to capture the flag and never let go of it.