Doom continues to surprise me. For example, the other day I jumped into a teleporter and was able to move again immediately afterwards. Usually when you teleport, you can't move for about half a second afterwards. How was this possible?
Firstly, no Boom trickery. Boom does have instant teleporters, but they're silent - no teleport fog, or sound effect - and they preserve orientation. But it wasn't one of those types, it was a regular teleport, in a vanilla map. It took a while, and a couple of jumps into other teleporters ("is something special about this particular one?") to realise.
The difference was that, in the map I was playing, the teleporter I had jumped into had put me into a damage sector, and I had thus taken a bit of damage. The function that applies damage sets a thing's "reaction time" to zero (with the comment "we're awake now..." or some such) Of course reaction times are for monsters, to stop them attacking too often and so forth. However, reaction time is also used for the post-teleport delay for players so of course, I teleported into a damage sector, took damage, and was able to move again, earlier than usual. It's a case of the same variable being used for two different purposes for two different classes of objects.
Now I wonder if it's ever been exploited in a speedrun, or even if I've noticed it before in any other maps but it just hasn't registered. Thinking about it I suppose you teleport into a damage sector at the end of episode 1, but into a small square from which you can't move, and it's pitch dark, and you die pretty quickly, so the lack of delay probably isn't noticable.