Here is the full list of all 18 Blade Ballet achievements.
Win a round as Nix.
Win a round as Syphon
Win a round as Steve
Win a round as Torque
Win a round as Vanguard
Win a round as Catbot
Win a round as Riot
Win a round as Ruckus
Win a round as Trigger
Win a round as Drop Jaw
This is secret for now!
Kill Riot while she has all of her shields
Cheat death with an invulnerability capsule
Kill a player by charging across the level
Win a round without killing anyone