Early warning system
Hey, you know what I love? Sneaking around all tactical-like and tripping my feet on invisible linedefs that open twenty six closets in an inconspicuous arena the size of a fucking golf ball. Oh, what's that, you crossed a linedef somewhere outdoors? Well don't mind if I raise half the map's monster pits. What do you mean you don't like to get your asshole prolapsed by an entire battalion of dangerously Irish hell knights? Are you some kind of noob who can't play Doom? Why, git gud, feggit.
If you trip a cross linedef that raises a fast ceiling, lowers a floor, or raises an instant floor, delay that action by no more than 4 seconds and notify the player to prepare vaseline or jump out the nearest window.
Voodoo dolls are going to be an absolute bitch. I'm calling it now.