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