Here is the full list of all 12 Grand Class Melee 2 achievements.
Complete 1 game
Kill 100 opponents
Win 10 games
Complete a 4-player game without any AI opponents
Watch 10 games in Spectator Mode
Win 100 games
Win against a team of 3 AI opponents
Win a round with a 1/4 heart remaining
Win a round without taking any damage
Raise your melee damage output to 10
Achieve max speed
Have 'Survived' as every class