MAP20: Gotcha! (Doom II)

MAP20: Gotcha! is the twentieth map of Doom II. It was designed by John Romero and uses the music track "Message For The Archvile". It is notable for including a possibility of monster infighting between a cyberdemon and a spider Mastermind.

Walkthrough
Go through the door at the start and clear the opposition there. While moving into a larger room, platforms will lower in the center of it revealing the Spider Mastermind and Cyberdemon (A). Try to lure them into a fight (moving in the west of the room behind a raised wall in the western platform). Defeat the remaining enemy using the platform as cover (B).

Hit the switch in the western platform and immediately eliminate the Arch-Vile and baron of hell that will come through the door (C). Afterwards, take the lift to go around the walkway and go through the door. Follow a winding stairway (D) down towards the teleporter. Go down another stairway and jump into the dark opening (E). Follow the corridor to the end and hop in the teleporter (F).

You will slowly go down into a small room with zombies and imps (G). Through the opening you will see a section of wall lowering across the lava pool (H). Wait for it to lower completely and jump through the opening. Follow the corridor, climb up the stairs and snatch the plasma rifle (I). Watch out for enemies popping out and run down the stairs towards the walkway and walk through the teleporter (J). In the last room, walking through the narrow walkway until the end and jump in the hole (K). Watch out for commandos and cacodemons.

Official

 * 1) At the very beginning of the level, turn around and face the structure behind you. Walk off the ledge you're on to cause a walkway to rise below you (L). Follow this walkway around to the back of the structure to access its inside. Once you're done exploring, drop into the pit of blood between the walkway and the structure. At either end of the semicircular pit are alcoves. The western alcove contains a radiation suit and a bulk cell and is considered a secret (M). The east alcove teleports you back to the starting point.
 * 2) In the northeast corner of the level is a large structure (N). Walk around the far side and you'll see a narrow "alley" with a glowing skull decoration at its end (O). Enter this alley to find a passageway leading up to a teleporter (P). Go through to be taken to a circular structure in the northwest of the map (Q). After raising the floor in this building, flip the switch to lower a teleport, but do not go through it yet. The walls immediately to the left and right of the teleporter can be opened as well (R). Both count as individual secrets.
 * 3) See secret #2.
 * 4) At the end of either secret #2 or #3, open the wall leading to the area behind the teleporter (S; the right wall in the left alcove; the left wall in the right alcove). This also counts as a secret and contains a soul sphere (T).
 * 5) On the east side of the map is a square building in a sunken pit of lava. Enter this building via the lift in the southwest corner and follow the winding path all the way to the teleporter at the top, but do not go through it (U). Instead, open the wall immediately to its left to reveal a secret path leading to another teleporter (V).
 * 6) Take the demon-faced teleporter in the area with the circular walkway (after the room with the battling Cyberdemon and Spider Mastermind). Follow the white walkway in front of you and run through the dark hole in the wall (W). Hug the left wall in this dark area and you'll go through a narrow tunnel with a teleport at the end. Go through to be taken to a tall pillar with a megasphere (X).
 * 7) Return to the dark area containing the passage to secret #6, but take the non-secret teleporter on the opposite end of the room (Y). Once the floor lowers, drop off the ledge straight ahead to lower the wall in front of you. Go through the newly opened hallway until you reach the dark room with a lit staircase in the center. The wall with the lightning symbol on the south end of this room can be opened, and contains a soul sphere (Z).

Non-official

 * 1) Shooting the left side of the structure above the demon-faced teleporter (this can be done either from the room containing secret #2 or from secret #6) opens a small alcove just to the left of where you find secret #2. It contains a BFG9000 and two energy cells.

Records
The Compet-N records for the map are:

Things
es:MAP20: Gotcha! (Doom II)