Here is the full list of all 15 Flag N Frag achievements.
Win a match in any league as the Mutoid Maniacs.
Win a match in any league as the Bubblegum Bandits.
Win a match in any league as Dropblock.
Win a 5 star match in any league.
Win a match in any league as Robo Mako.
Win a match in any league as the Rom Robbers.
Win a match in any league as Slam N Jam.
Win a match in any league without losing a single unit.
Win a match in any league as Swamp Chomp.
Win a Mutant League match against 3 computer opponents.
Win a battle without any of your Peg Blocks touching the computer opponent's Bullet Ball.
Win a match in any league as the Food Fraggers.
Win a Pro League match against 3 computer opponents.
End a match in Turbo league with over 99 Cheat Coins collected in total.
Win a Turbo League match against 3 computer opponents.