Here is the full list of all 17 Tower of Guns achievements.
Pick up Four Difficulty++ Badges in a Single Life
Die while a Boss is Exploding
Complete a Stage Without Anything but the Boss dying
Complete a Stage without Picking up ANYTHING
Complete a Stage After Firing Exactly Fourteen Shots
Discover the Secret Code
Unlock all the Perks
Unlock all the Guns
Pick up 1000 Health Items While at Full Health
Kill That Dang Wall of Turrets Three Times
Reach Endless Stage 14
Jump and Remain Airborn for 45 Seconds
Accumulate 888 Gold In a Single Run
Tilt 10 Times in a Single Stage
Stomp a Hugbot to Death
Find and Level The Motivator Gun to Level 5
Kill over 350 Mobs in a Single Level