This achievement is unlocked for completing the mission Army of Darkness
This is the 5th and final mission in Episode 3: Beyond Berlin and the final mission of the
game.
*** Spoiler - click to reveal ***When you face the giant Hitler, break through the door on the left. Go up the stairs and shoot the skulls floating around another door.
When you get inside this door there will be a skeleton on the floor. Pick it up and go back down the stairs (or jump out the window facing Hitler) Throw the skeleton into the pit where Hitler is. He will return to normal size and he will stand at the podium. Headshot him and he will return to the pit.
Now break through the door on the right and repeat the skeleton thing.
The 3rd and final skeleton will be behind hitlers podium on the top floor.
There will be alot of heavy and armored enemies. And Hitler will continue to spawn zombies. So speed is critical.
All done