Here is the full list of all 44 Underhero achievements.
You deserve a raise
All weapon Upgrades!
Defeated ???
The End of The World
Defeated Mr. Stitches
Spared the Masked Children in Heroes Road
All HP Upgrades!
Eased a Fathers Mind
All Music Cassettes
Bribed 20 Enemies
Recruited The Baron
All missing keys used
Recruited the Moth Queen
All Shield Upgrades
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
Found the Hidden Treasure of the beach
Cleared the Pica Pica Coliseum
Half weapon Upgrades!
Defeated Baron van Gregory
Defeated The Grey Kid
Won the Ice Skating Competition
Half HP Upgrades!
Completed the Bros Quest
You gave Blobber his favorite drink
Made your first drink
Your First Bribe
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
Finish the Intro