Monster Heights?

[Jarvy]

So, monsters have set heights values that determine whether or not they can fit in certain gaps, but in a video I was watching, it said doomguy can never jump over a monster because their collision box is infinite. So, there's a height for collision with walls and a height for collision with other entities? Or did the video just lie? Could someone please explain how monster height/collision works?

[Shepardus]

Monsters and other things have heights (the values of which can be found on the Doom Wiki if you care to know), it's just ignored in a few specific cases. The heights are still relevant for stuff like collision with terrain as well as passing under/over projectiles.

Worth a watch: