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