Here is the full list of all 22 Langoth achievements.
Start a new game
Kill the first boss
Complete the first level
Collect all the bonuses on the first level
Kill all the enemies on the first level
Kill the second boss
Complete the second level
Collect all bonuses on the second level
Kill all the enemies on the second level
Find the secret level
Complete the secret level
Kill the third boss
Complete the third level
Collect all bonuses on the third level
Kill all the enemies on the third level
Watch credits
Stay in air from 1.8 to 1.9 seconds
Complete the game for Adam
Complete the game for Eve
Collect all the bombs on the first level
Collect all the bombs on the second level
Collect all the bombs on the third level