Here is the full list of all 41 OTTTD achievements.
You got an employee to level 99. We're impressed and a little scared
3 star every mission. Show off!
Watched the credits to the end without speeding them up
Finish a mission with 5 Shield Emitters or 5 Healthenators
Finish the game
Wage war across 10 separate days
You're making us all look bad. A HEROCORP™ employee reached level 50
Double-killed the zombie shark and his buddy
Killed 9001 enemies with little to no remorse except for that one guy... he was cool
Defeated the Kraken and lived to tell the tale
Finish a mission with <10% HQ health. Good luck filling out the paperwork back at HEROCORP™
First HEROCORP™ employee with over 3000 health gets a discount on their insurance
Earned total 1 million coins
Finish a mission by only building rocket towers
Revive a HEROCORP™ employee
Fully upgraded the Deathbeamer
Earned 42 stars
Finish a mission without building any towers
Unlock all HEROCORP™ employee classes
Max out a single skill for a HEROCORP™ employee
Nobody likes a show off. A HEROCORP™ employee reached level 20
At least one skill point on all abilities for a HEROCORP™ employee
Play the game 3 days in a row
First HEROCORP™ employee with over 1337 damage gets a ribbon
Spent 100,000 coins and kept all the receipts for accounting
Bought your first weapon
Spoilt your employee with the most expensive weapon
Well thanks for putting in the effort. A HEROCORP™ employee reached level 10
Finish a mission without upgrading any towers
Earned 21 stars and a free meat tray back at HQ
Killed the flying shark or understood our movie reference
We shouldn't reward you for letting an employee die. Looks like Steve in HR has some explaining to do
Give yourself a pat on the back. A HEROCORP™ employee reached level 5
Finish a mission with perfect HQ health
Killed 300 enemies, looked ripped while doing it
Completed HEROCORP™ training
Earned 5 achievements
Earned total 10,000 coins
Fully upgraded a tower
Earned first 3 star rating on a mission
You earned your first level up