Here is the full list of all 18 Gravity Badgers achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Lose to any boss.
Play the game for a total of ten hours.
Get all Energy Cores.
Finish the game.
Play the game for a total of five hours.
Defeat the fourth boss.
Defeat the fourth boss with a perfect score.
Defeat the third boss.
Defeat the third boss with a perfect score.
Play the game for a total of one hour.
Defeat the second boss.
Defeat the second boss with a perfect score.
Get 150 Energy Cores.
Defeat the first boss with a perfect score.
Defeat the first boss.
Get 75 Energy Cores.
Finish all 9 Tutorial levels.
Collect 3 Energy Cores in any level.