MAP31: DejaVu is the secret level of Memento Mori II. It was designed by Orin Flaharty and uses the music track "Bavor The Mad" by Mark Klem. The title name comes from the French expression "deja vu", the psychological sensation that you are repeating a situation already seen or witnessed in life. Deja Vu is designed in a techbase style reminiscent of Doom's Knee-Deep in the Dead, hence its title, which comes from the French expression "deja vu", the psychological sensation that you are repeating a situation already seen or witnessed in life.
In the eastern hallways accessed by the first switch, press upon the wall west of the northern light in the southern hallway to find a secret room (sector 55) with nine health bonuses and a berserk pack.
After going through the blue keycard door, open the wall in the northern inset to find a secret hallway (sector 144). Use the elevator to reach a room with a trooper, two (one on easy skills) sergeants, (a demon on hard skills,) four rockets and two stimpacks.
Open the northern wall of the secret hallway from secret #3 to access the outdoors area to the north. Go to the southernmost window (eastsoutheast of secret #1). There is a misaligned texture on the eastern wall. Open it to find a soul sphere (sector 170).
In the red keycard room, there is an arrow made of armor bonuses pointing at a computer panel. Press on it, and the mainframes to the east will lower to reveal secret compartments. The north and south compartments both contain a few monsters and each a stimpack; the central one (sector 224) contains two rockets and a rocket launcher and counts as secret.
Once you enter the southern computer room with the glowing lights (north of the yellow keycard), head into the inset to the northeast and you will find a lone barrel in front of a computer panel to the east. Destroy it and open the panel behind to find a computer map (sector 222).
From secret #6 backtrack your way to a room with four holes in the ceiling. Go west, upon entering another room with similar holes in the ceiling, run northwards to the elevator's east to find that a door has opened to reveal a nukage pool. Cross the pool and you will find a stimpack and a platform (sector 169) with eight armor bonuses, a backpack, a light amplification visor and a door. Enter this door to find another door that requires a yellow keycard. After grabbing the yellow keycard, return to this area and open the door to find a hallway leading to an exit switch that takes you to the super secret level, MAP32: Dances with Demons.
On hard skills it is only possible to obtain 99% kills in this level, as one imp (thing 349) contained in one of the inaccessible monster storages (sector 252) (which store monsters for teleportation into the level) is glued to a barrel (thing 383) occupying the same space. Whether this was intentional or not is unknown.
Unlike another level from Memento Mori II designed in Knee-Deep in the Dead style, MAP24: Io Lab, this level features only Doom monsters. In fact, in DejaVu there is even more restraint than in MAP08: And the Dead Shall Rise from Memento Mori, also designed by Orin Flaharty, as lost souls and cacodemons are also missing. This means that in this secret level the player can only encounter monsters from Knee-Deep in the Dead. Regarding weapons and equipment, the design is slightly less consistent: megaspheres or super shotguns (from Doom II) are absent, but the player can collect a plasma rifle or an invulnerability sphere (present in Doom, but not in its first episode).