Here is the full list of all 20 Skyward achievements.
Time Survived - 3 Minutes
Time Survived - 5 Minutes
Time Survived - 10 Minutes
Score Achieved - 10
Score Achieved - 50
Score Achieved - 100
Threats Dodged - 100
Threats Dodged - 250
Threats Dodged - 500
Overall Score Achieved - 100
Overall Score Achieved - 250
Overall Score Achieved - 500
Number of Attempts - 10
Number of Attempts - 25
Number of Attempts - 50
Fall Out Of The World
Obtain Health Drop When Full Health
Collide With A Missile 25 Times
Collide With A Mine 25 Times
Collide With A Health Drop 25 Times