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