I managed to nail the Zero Press on Doom 2 MAP15 last night:
It took a while to figure out the exact position to hit the switch, but after working that out it's surprisingly easy to do and fairly consistent.
The way you're supposed to do this is to fight through the yellow key area, which involves going through the inside area, hitting a switch to activate some stairs, then crawling up to the battlements and pressing a switch to open a door on the first floor, then collecting the blue key from inside the door. Along the way are some awkwardly placed enemies that tend to get in your way and make it difficult to do the necessary backtracking to get the blue key. It's slow enough that it's faster, easier, and more consistent to open up the secret exit and go through the first secret level.
The Zero Press (discovered by the runner Zero Master) takes advantage of several quirks of the Doom engine to hit the switch from the ground level.
First of all, height is not accounted for when checking for activation. If a switch is 10000 units above your head you can still press it as long as it's within your activation range. Second, two-sided linedefs do not block activation, making it trivial to hit switches through a ledge if they're positioned right (hitting the exit switch in E2M2 in the slime and activating the secret exit switch on E3M6 are two popular examples of this in action). The thing that's initially tricky about the MAP15 press, I suspect, is the distance between the player position outside of the "castle" area and the switch itself. The positioning is precise, but there's enough clues on the texture to help you line it up.
Basically, you go to the far wall, turn right, go right around the middle, find the fairly noticeable texture seam and move 3.5 texels to the right of that. Face the wall at such an angle that you move very slowly to the left, hold forward, and mash spacebar until you hear the switch press sound, then run into the castle, pick up the blue key, and complete the level normally.
Feels good, man.
