Here is the full list of all 21 Fatal Theory achievements.
Beat Donatello
Beat Vlad
Start Story Mode
Beat Matt & Adam
Beat Giancarlo
Beat Spectre
Beat Punchy Mech
Beat Johnny
Beat Lilith
Unlock Umbrella (not the cheat way)
Max level up Vlad the Impaler
Max level up Baseball Bat
Max level up Whip
Max level up Swords
Max level up Guantlets
Max level up Umbrella
Max level up Black Blade
Max level up Nick
Beat Arcade
300+ on Survival
999+ Hit Combo