Here is the full list of all 20 Shadow Warrior Classic Redux achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Finish "Twin Dragon" expansion
Finish "Wanton Destruction" expansion
Finish any level faster than 3D Realms time
Finish "Code Of Honor" episode
Meet Sailor Moon
Find 70 secret areas
Defeat Sumo Demon boss
Collect 50 fortune cookies
Watch TV in Seppuku Station
Win 10 Pachinko games
Slice 100 evil ninjas with Katana
Defeat Serpent God boss
Finish "Enter The Wang" episode
Find Monty Python and The Holy Grail reference
Kill 500 enemies
Fire Nuclear Missile
Breed the rabbits to exhaustion
Hit 20 enemies with a vehicle
Use the Speed Racer RC car
Kill 50 enemies