Memorable placement of limited low-level enemies

[SPG]

I'm sure folks here could give examples of memorable powerful enemy encounters in Doom, and/or overwhelming numbers of enemies. For this thread, though, I'm curious about low-level enemies that stuck out to you, not because there were a hoard of them, but because they were placed in such a particular way as to stick with you. Maybe that placement made them harder than they'd normally be, maybe they gave a good jump scare, maybe it was just bonkers.

An extremely vanilla example that comes to mind for me is in E1M3, when the lights go out after getting a key and a monster closet opens behind you with imps.

[Xyzzу]

that one joe-ilya map where there's a single zombieman and the map crushes you if either of you shoot:

 

Edited May 9 by Xyzzу

[8088mph]

Those little imps (in E1M3 I believe..?) that pop out when you collect a blue key is such an iconic way to introduce monster closets.

Edited May 9 by 8088mph

[kalensar]

My favorite one would be the entirety of Map01 of Hellbound.

[ivymagnapinna]

Crumpets map03 has just 36-37 monsters depending on the skill level, on top of being very physically small, but it really stuck in my memory I think because of that. Very compact and tightly built.