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