The Revenant Problem

The Revenant Problem is a joke WAD created in 2017 by Revenant100, also known as MarphyBlack, whose previous works include other revenant-themed joke WADs. The Revenant Problem parodies the philosophical dilemma of the ; each map has two groups of monsters trapped by explosive barrels, and the player must choose which one they wish to sacrifice.

How to access the secret level
In MAP15, the destinations are entirely empty. If the player looks to their right, they will find an eyeball switch blocked off by bars with skulls on them. This is the exit to the secret level. Interacting with the bars will tell the player they need all six keys to open them. If the player waits for about one minute and ten seconds, they will receive a message saying "I like this song, too." If they wait another minute (for a total of 2 minutes and 10 seconds), they will receive another message saying that they "magically" acquired the keys. They can then open the bars and head to the secret level.

How does this work? Behind the revenant's path is an out-of-bounds room containing a voodoo doll on a conveyor belt. Blocking the doll are two walls that slowly rise up. When the first wall is high enough that the doll can pass through (at 1:10) it will pick up a small cell pack, displaying the "I like this song, too" message. At the 2:10 mark, the second wall rises high enough, allowing the doll to pick up the keys and deliver them to the player's inventory.