Here is the full list of all 20 MOTHERGUNSHIP achievements.
Kill 1000 Spinbots
Complete mission without taking any damage
Complete a mission without killing anything except the boss
Find 15 secrets in a single mission
Get 40 jumps in a single run
Kill 5 mobs in one shot
Fire 65535 shots
Complete a nightmare mission without equipping any gun
Add part to a gun 1000 times
Craft a gun with DPS of over 100
Build a gun that uses over 20 parts at once
Finish 1000 enemies using your fist
Survive 30 challenge rooms
Reach room 20 in Endless
Complete the campaign
Equip 10 armor upgrades
Die from lava damage after killing a boss
Take 4 diceroll rooms in a single mission
Complete a mission without missing a single shot
Complete your first mission