Here is the full list of all 20 Space Robot Samurai Zombie Slayer achievements.
Take No Damage for 1 Minute
Clear the Screen
In This Game You Kill Zombies
Get a 99x Streak
Get 100000 Points in a Single Game
Survive for the Entire Song
Survive for a Wave
Take 100 Damage in a Single Game
Kill 1000 Zombies
Get a 50x Streak
Get 10000 Points in a Single Game
Take 50 Damage in a Single Game
Get a 10x Streak
Get 1000 Points in a Single Game
Kill 100 Zombies
Get Killed With 10 or Less Points
Kill 1 Zombie
Kill 10000 Zombies
Kill 20000 Zombies
Accumulate 1000000 Points All Time