Here is the full list of all 22 Willy Jetman: Astromonkey's Revenge achievements.
Hunt 500 cyan Floaters
Defeat Astromonkey at sector 1-7
Complete Wyrm's Labyrinth
Find 20 secret areas
Mow 1000 plants
Get a X50 combo
Defeat Astromonkey at sector 2-3
Kill WC Worm
Get 100K credit
Get all weapons
Get all gears
Complete Dragon's Jaws labyrinth
Hunt 5 red dragons
Get the Legendary Weapon
Get the Flamer max level
Hunt 200 orange Floaters
et the Dr.One max level
Find all Golden Idols
Reach Willy's max level
Defeat Fusionbot
Get the Bat-Willy suit
Finish the game in 3 hours