Step 0: In the Title Screen, go to Options and check Can Win the Game. Start the game.
Step 1: Exit the beginning area by using the key on the lock.
Step 2: Take the strange artifact near the coffin.

During these steps, press E near any pots that you can find. You might save some time on preparation.

Seriously, from this moment forward, picking up any keys will activate Greg to roam. He will bang on his coffin but he won't be able to come out until you pick up your first key. Below I will list what preparation to do. Mentally note down where all keys are and memorize where to get them.

In the lever room, switch the levers to this configuration, with orientation being from when you enter the lever room (R means lever pointing to Right, L means level pointing to Left)

LRLRLR
LLRRRL
LRLRLR

From there, you can walk across the bridges starting from the right going forward, then taking left, and forward to the ending ledge of the room. DO NOT PICK UP THE KEY. Instead look for a Tome and leave. Note where the second key is, which is on the floor below and maybe under the second bridge to last bridge you cross exiting the room. It glows, so look for a glowing spot.

To the left of the four key holes in the main room is the Stone Room. Here, there are three blocks stacked on top of each other and a correct permutation is needed to unlock the key. These symbols can be found in The Maze, but we're too busy to be nerds looking at symbols so we're going to force the lock. Rotate the top 3 times, the middle 2 times, and the bottom 3 times. DO NOT PICK UP THE KEY. Instead, go to the Maze. If a Tome is in this room, pick it up and head out.

Now, if you don't want to wander around like a chicken with its head cut off, I suggest heading over to this guide.
That is a guide with all the maps you need to navigate the maze, and will tip you off to any tomes that you may have missed. If you enjoyed that guide, give them five stars.

The maze is very confusing. The maze is 3 layers. Presumably this is supposed to match the Stone Room, but don't worry about that. Check each layer (searching for the tomb, if you haven't found it yet) and you will be looking for a little alcove. Inside is a key. If you have not found the tome, search for the tome and make your way back to the key room. Otherwise, it's time to execute our escape plan.

Starting this section, you should be in the Maze next to a key, and have grabbed the 3 tomes.
The tome names are as follows:

• Tome of Perdito Tempus
  
• Tome of Foetor
  
• Tome of Stercus

BEFORE YOU START, once you start to pick up keys Greg will spawn and start to get faster. It is RECOMMENDED to use the following movement tech: Move diagonally and sporadically press the sprint button. This will ensure you have maximum speed to outrun and kite Greg as you are moving through obstacles.

Now, let's start.

First, grab the key and escape the maze. Easier said than done, but don't worry as Greg shouldn't be after you yet. Make your way back to the Coffin Room then run into the Stone Room. Grab the key there, and go back to the Coffin Room. Quickly make your way to the Lever Room and cross the platforms to the other side of the room and grab the key. Make your way back across the platforms and drop down where you found the other key. Then make your way to the staircase (it should be on the rightmost side of the room, if you're running back) and make your way to the keyholes.

The order in which you put the keys in SEEMS to matter (for luck, put them in as 3 1 2 4, from left to right). Pushing them in should activate the secret exit in the maze.
Reports indicate that the exit can be found in the following locations:

• In the Stone Room behind the Pedestal.
  
• In the Lever Room at the far end, to the left of the pedestal.
  
• In the bottom level of the Maze.
  
• In the middle level of the Maze, in a very long corridor.

Place each of the tomes on the pedestals, and the exit will open.

Now go rub it in Greg's face.

Thanks to the following steam members for helping to crack the puzzle and help YOU win the game:

EL REY DEL SERVIDOR and CellarPhantom for finding the location of the secret exit.
KektusBOD (and many others) for the tip of moving diagonally and sprinting to move faster.
gristCollector for finding the easier Stone Room solution.

At this point, you should only play further if you want 100% of achievements.

To enable nightmare mode, start the game and click options. Enable Can Win Game, and The Greggening. This will take more tries than in normal mode, but if you efficiently kite Greg and company this strategy CAN work.

I recommend the following: from the maze, collect the key and insert it into its slot. Go to the lever room, and travel across the bridges and get the two keys, and insert them into their slots. Then go to the stone room, grab that key, insert it into the last slot. Then HOPE that the exit appears in the stone room.