It sets the actor's hit points (extra) to 0.
It sets the actor's damage type (htpicnum) to SHOTSPARK1 (bullet).
It sets the actor's damage (htextra) to 1.
This will make the enemy die, regardless of how many hit points it had. Note that the falling height which triggers this is not very high -- even falling from the secret RPG to the ground in E1L1 will trigger it.
This is problematic because:
- Falling damage is not appropriate for some enemies (including some enemies that actually do "fall" using the CON command)
- It's an insta-kill, so even if fall damage were desirable, infinite damage is not typically desirable
- AFAIK There's no flag or other nice means to eliminate the damage. You either have to not use the CON fall command, or you have to detect and circumvent the damage by monitoring certain structs before the actor calls ifhitweapon and then reset hit points to the amount from the previous tic
I'm also not sure if the feature is working as intended. I looked at the source for the fall command and found some code that does something similar, but it looks like it has some extra conditions in there which were not being met by my falling enemies. One other thing I'd like to point out is that there are various hardcoded differences between enemy and notenemy. In general, enemies move around and clip better, so it's not desirable define an actor as notenemy.
EDIT Additional notes: I do not know if the hardcoded fall damage is applied to the original Duke 3D enemies, or only to custom enemies. I also don't know if the feature is in DOS Duke, or if it was added to EDuke32 later. If it was added later, then it surely is affecting various mods in a bad way.