Sometimes monsters like stairs, and sometimes they don't. What's up with that? Why is that some monsters struggle to get down a set of steps, and others just walk right down uninterrupted? Hopefully this visual will help.
Like the player, monsters can only climb up steps at a maximum height of 24. The difference between monsters and players, however, is that they can only descend from steps if they are a 24 height. The caveat however, is that they cannot cross too many steps that descend below 24 units if their entire bodies can't fit over them.
Lets say Mr. Spookybones wants to walk down these steps. The revenants bounding box is 56x56 units. The steps are only 32 units deep. If the steps are each a height of 16 units, Mr. Spookybones will not be able to cross over the first step because his bounding box cannot fit within the first step. The addition of the next 16 unit step would be a drop of 32 units, and the revenant cannot fall that far, so there may as well be a fake wall between him and the next step.
You could however, make the steps a height of 8, and the revenant will be able to step over at least 3 of the steps (3 x 8 = 24). The skeleton's entire bounding box should be able to fit over at least one of the steps, so he falls enough to make the following steps a little easier to step over.
You could also make the steps 64 units deep, the revenant can descend the steps one at a time.
So there you have it. If you can't figure out why your stupid monsters dont want to walk down your stupid stairs, this is probably why.
Knowing this helps enemy placement in regards to confining them into certain locations without using block monster lines. Doing it that way for example you can raise sectors later to subtly allow monsters to be able to get off their confinement and turn a once thought of harmless monster into a cunt who is now chasing you down at a certain point in a map. Good tip this one 40, I imagine quite a few would struggle with this.