Here is the full list of all 17 Powerless achievements.
An ace up your sleeve
Kill some things
Kill lots of things
Kill everything
Kill 15 enemies at once
Play a game that lasts at least 2 hours
Play a game that lasts at least 3 hours
Beat Purge mode on Wuss difficulty
Beat Purge mode on Veteran difficulty
Beat Purge mode on Badass difficulty
Beat The Gauntlet on Wuss difficulty
Beat The Gauntlet on Veteran difficulty
Beat The Gauntlet on Badass difficulty
Survive for 1 hour on Wuss difficulty
Survive for 1 hour on Veteran difficulty
Survive for 1 hour on Badass difficulty
Kill 1000 enemies with your katana