Linedef type 257, Quicksand, is a type of floor over floor block which the player will sink into. It can be used to create sand, mud, or any other sludgy material that the player will be pulled into on contact. The player can escape the quicksand simply by jumping many times. However, normal jump height is greatly reduced in quicksand, so any ledges near the quicksand that are meant for escape should be low enough for the player to jump onto. Sinking deep into quicksand alone will not harm the player, so death pits are normally placed under the quicksand so the player dies if they sink too deep. The player can sink right to the bottom of the quicksand and fall out of the bottom if it is placed above the sector floor, so it is possible to make secret areas or even alternate routes under quicksand, à la Sandopolis Zone from Sonic 3 & Knuckles.
Setup
The flats, floor height, and ceiling height of the FOF are determined by the flats, floor height, and ceiling height of the control sector, and the sidedefs of the FOF's walls are determined by the sidedef of the control linedef.
The light level of the control sector will determine the brightness of the shadow cast by the FOF. If the light level of the control sector is lower than that of the target sector, then it will cast a dark shadow. If the light level of the control sector is higher than that of the target sector, then the FOF will illuminate the area below it. If the light level of the control sector is equal to that of the target sector, then the FOF will not affect the light of the area below it.
The player's sinking speed and movement reduction are determined by the linedef's X distance and Y distance, respectively. The X distance determines how fast the player sinks into the quicksand. The greater the X distance, the faster the player sinks. If the linedef's X distance is 0, the player does not sink at all. Specifically, 70 fracunits of X distance equal 1 fracunit per tic of sinking speed. The Y distance determines the "sludginess" of the player's movement while he is in the quicksand. The shorter the Y distance, the slower the player moves. If the linedef's Y distance is 0, the player is completely unable to move while in quicksand. If the Y distance is higher than 50, the movement instead becomes "slippery", as though the player is walking in oil. However, this is not recommended, as the physics are unrealistic.
Note that if the control sector is set up improperly, the player will sometimes sink only a few units into the quicksand; this issue can be remedied by reversing the direction of the linedef.
Checking Flag [10] / Repeat Midtexture / Effect 5 will cause the flats of the FOF to "ripple", similar to the effect you would see inside a water block.
Linedef special info
Floor height
Height of bottom of FOF
Ceiling height
Height of top of FOF
Sector light level
Brightness of shadow cast
Linedef X distance
Sinking speed of player (1 FU/70 tics per FU distance)
Linedef Y distance
"Sludginess" of player's movement (If 0, player cannot move; if more than 50, movement becomes "slippery")
Linedef flags
[10] Repeat Midtexture / Effect 5: Flats use the "ripple" effect
