Alright, Linedef Type 89. This isn't covered on the Wiki, as well as being overly confusing on Specials List, so I'll give you a brief explanation on use.
You want 3 small control sectors
that are connected. You want them all to be squares. Once done, you want the sector in the center to have type 89 in use. Now, you want the center control sector, and the control sector to the left to have the same sector heights for the ceiling and floor.
(The control sector setup should look like this:
http://dw.sepwich.com/images/SRB2/linedef89.png
Note: That is
extremely zoomed in. The control sector's linedef with the effect is only 32 units wide.)
Now, you want the control sector to the right to be the height you want the elevator to stop at. But, you want the difference in ceiling and floor to be the same as the other two sectors. (Say, the two first control sectors have a floor height of 16 and a ceiling height of 36, and you want it to rise 100 units up, you'll want the floor at 116, and the ceiling at 136). Finally, note how, in the picture above, the right-handed control sector has a shorter linedef at the top. This is because the length of that linedef adjusts the speed. Changing that will speed up or slow down the elevator. Experiment and see what you want.
Note that the sector brightness of the elevator applies below the elevator here. I'm not sure which of the three you would adjust for that, so you could set the brightness level the same on all 3, and it'd apply.
