Here is the full list of all 38 Erroneous achievements.
Play Erroneous before it was Free-To-Play
Snipe someone from across the Map
GIB somebody
Snipe someone from across the map without using a Sniper
Kill someone after you die
Taunt after Losing
Taunt after Winning
Die Zero times during a match
Kill Zero people during a whole match
Switch teams in-game
Jump into the BaezResort Volcano
Rickroll an player
Join a Friend
Turn on Cheats/Commands in a game
Win your 1st game
Win your 10th game
Win your 100th game
Win you 420th game
Lose your 1st game
Lose your 10th game
Lose your 100th game
Taunt for your first time
Taunt 1000 times
Play with more than 400 bots
Kill a Teammate
Kill 100 Teammates
Kill 1000 Teammates
Kill somebody
Kill 100 people
Kill 1000 people
Die
Die 100 times
Die 1000 times
Find the Golden Weapon Cheat Code
Find the Rickroll Cheat Code
Find the Realtime Daylight Cycle Cheat Code
Find the Sans Sniper Cheat Code
Play a game with one of the Developers