Here is the full list of all 20 STAY achievements.
The base game contains 12 achievements, and there is 1 DLC pack containing 8 achievements.
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Survive for 5 Minutes in a single Lethal test
Survive for 15 Minutes in a single Lethal test
Complete a Speedrun test in less than 5 Minutes
Complete a Speedrun test in less than 8 Minutes
Complete the Phase 5 on a single Wave test
Complete the Phase 10 on a single Wave test
Unlock all the other achievements