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