
This is an image I made for the wiki, as a colorful way to illustrate how many monsters there are per level. I didn't do this legitimately, but after thinking about it a bit, it isn't completely impossible to do. A goblin character with a Yendor prep and access to Glowing Guardian could probably do it.
So my challenge to us all is to go ahead and do it, and on as many maps as we can. Many maps have complicating factors such as subdungeon monsters and weird scripted events. I'll leave it up to the submitter to decide how to handle such things. The only hard and fast rules are
1) Every kill must match your level
2) You must have at least one kill per level.
3) Not a rule, but it is more impressive if you manage to kill everything.