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