Here is the full list of all 44 Underhero achievements.
You deserve a raise
Defeated ???
Defeated Mr. Stitches
The End of The World
Spared the Masked Children in Heroes Road
All HP Upgrades!
All Music Cassettes
Bribed 20 Enemies
All weapon Upgrades!
Recruited The Baron
Found the Hidden Treasure of the beach
Recruited the Moth Queen
All missing keys used
Eased a Fathers Mind
Defeated T. Bur
The Show must go on
Read all Robot Text Logs
Night Theater
Defeated El Salserissimo
Cook the spiciest salsa
Complete Jilani'snPepper Collection
Half Music Cassettes
Cleared the Pica Pica Coliseum
Defeated Baron van Gregory
Half weapon Upgrades!
Half HP Upgrades!
Won the Ice Skating Competition
Defeated The Grey Kid
You gave Blobber his favorite drink
Completed the Bros Quest
Made your first drink
All Shield Upgrades
First Shield Upgrade
First missing key used
Defeated The Moth Queen, Alexandria II
A tree full of beer
First weapon Upgrade!
Killed 20 Enemies
First HP Upgrade!
Won the Ant's Gang Race
First Music Cassette
Killed your First Enemy in Combat
Your First Bribe
Finish the Intro