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