Here is the full list of all 31 STHELL achievements.
Die 50 times
Destroy 50 Breachtrons Model V-104H
Defeat the third boss using the Shotgun only
Destroy 10 Spidertrons Model S-682T
Destroy 25 Houndtrons Model B-55H
Destroy 5 Mobile Barriers Model B-086E
Defeat the second boss using the Semi Automatic Pistol only
Destroy the Mantis Prototype Zero
Destroy 200 Drones Model K-88A out of a swarm
Destroy The Monolith Prototype Zero
Defeat the first boss using the Semi Automatic Pistol only
Destroy The Tripod
Get the PPR
Destroy the Spider Sentinel Model S-900T
Destroy 15 Bipeds Model V-655R
Die 25 times
Get the Heavy Machine Gun
Survive 3 minutes with your health under 30
Stay alive for 10 minutes
Get the Energy Gun
Get the Revolver
Destroy 30 Bipeds Model V-107Q
Stay alive for 5 minutes
Destroy 50 Pathfinder Model P-003E
Destroy 50 Rollers Model K-4M1KZ
Destroy 50 Drones Model F-284G
Destroy 10 Cargo Mechas Model D-808E
Destroy 100 Breachtrons Model V-004H
Get the Brute
Die for the first time
Get the Shotgun