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