Where the Twist Flops is the twenty-third level in Marathon 2: Durandal. It is the first level of Simulacrums, the eighth chapter of the game. The human survivors on Lh'owon have retreated to this deep underground facility, and they are being attacked by the Pfhor. The newly-awakened S'pht AI Thoth sent you here to eradicate the Pfhor and deal with the Simulacrums here as well, who have infiltrated the ranks of the BOBs.
The level is filled with many BOBs, some of which are exploding ones. There are also numerous S'pht Compilers and Pfhor Hunters.
There is one pattern buffer in this level, which is located in the starting room. In a large gallery in the northern part of the level, a 1x shield recharger can be found. Another 1x shield recharger is located a little further to the east, in a room directly below a large ammo cache. The southeast part of the level contains a 2x shield recharger.
Walkthrough[]
In this level, you'll have to find and kill all Pfhor and Simulacrums. There's a pattern buffer at the start you can use, but getting to a shield recharger is a bit harder.
The easiest shield recharger to reach is found when you go north from the pit of captured BOBs. Follow a wide gallery all the way north, drop down into the next gallery, and go to the south end to find a 1x shield recharger. A switch next to the charger takes you back to the beginning of the level.
If you go east from the pit of BOBs, you'll find a large circular room. East of that is a four-way intersection. The south corridor here leads to a 2x shield recharger, while the north exit leads to a large cache of ammo with also contains a WSTE-M5 Combat Shotgun. There are narrow shafts in the floor of the ammo cache room through which you can drop down into a lower room with a 1x shield recharger at the north end.
Once you have cleared the level of enemies, return to the starting room and read the terminal to be teleported to Beware of Abandoned Rental Trucks.
Secrets[]
A hidden, submerged terminal can be found at the north end of the lava pool just north of the pit of BOBs. There's an invulnerability powerup in front of it. See the location marked 'A' on the map.
Terminals 
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@%(Ufevil3%&~FF`fx[]
This terminal has a message from Thoth, who tells you to "crush the slavers". When you're done with that, Thoth proclaims that he understands Durandal's purpose; to find Thoth's creators (the lost S'pht clan) and get them to help free the S'pht from slavery. Thoth then sends you to the next level to activate some sort of communications technology to contact the lost clan.
ABANDONED HOMEWORLD FOR SALE, CHEAP!!![]
This hidden Easter egg terminal contains a few classified advertisements for things that are up for sale. These include the UESC Marathon (this ad was taken from a similar terminal in Marathon 1), the planet Lh'owon, and a 1985 Toyota Corolla.
Sources[]
Marathon 2: Durandal - Level 23: Where the Twist Flops