Here is the full list of all 22 In Space We Brawl achievements.
Complete 1000 fights
Kill 250 players with the Plasma Sword
Collect 5 defensive pods at the same time
Kill 50 players without using weapons
Fire 500,000 shots
Kill 2,000 players
Kill 4,000 aliens
Kill 250 players with the Quantic Slinger
Obtain Old School achievement 50 times
Play 100 mirror matches
Complete 10 matches in less than 3 seconds
Commit suicide 50 times
Win 25 1 vs 3 matches
Fight in every single sector of each location
Complete all the 21 challenges
Complete all the challenges with S rank
Unlock the 5th challenge
Unlock the 10th challenge
Unlock the 15th challenge
Unlock the 21th challenge
Complete all weapons challenges
Complete all spaceships challenges