Here is the full list of all 18 LEGO Brawls achievements.
Be named Top Brawler 20 times
Master the Janitor Champion
Play 20 Brawls
Win 5 consecutive Brawl matches
Be named Top Brawler 5 times
Create 3 custom brawlers
Play 5 Brawls
Play your first game in Party Mode
Be named Top Brawler
Play your first Brawl
Customize your Loadout
Customize your first Brawler
Play 5 games in Party Mode
Master the Cowgirl Champion
Master the Owen Grady Champion
Master the Mummy Queen Champion
Master the Punk Pirate Champion
Master the NRG Nya Champion