I think there's a bug with enemy colors. Sometimes the regular purple foot soldier will appear blue or red, but behave like regular purple puncher, just the wrong color.
So, change the dynamite thrower color to red to match the arcade. Could be simple. Although the dynamite throwers from behind the wall are purple in the arcade
Change mouser detail color from blue to red to match the arcade. Could be simple too. Although there are blue mousers on the arcade that don't shoot lasers? Sounds like an arcade region thing, I'm watching a longplay and they are all blue, but I do remember seeing them red.
In the arcade the one that throws knives is white, not blue.
Placement: not so simple, haven't figured out enemy placement yet, seemed a bit complicated.
Mousers shooting lasers: complicated XD
I think these aesthetic changes or arcade like changes should be a sepparate patch, they don't go in the direction of the Options menu patch. But I'm not sure I see too much value in those because the differences between the NES and arcade versions are so big that those are just very minor details by comparison.
I did think about a running move. This game kinda wants that. But anything that adds more graphics is out of the question for me, since all CHR pages are packed and I don't want to expand the ROM.
I wanted to fix the 2 hit single move bug when you're spawning. I couldn't figure it out.
The crazy ideas are for the "new" fighting option, but too crazy for me for now:
Add that slow normal attack that connects twice to the arsenal by pressing down+attack.
Or... Add a combo system. B B B B = "normal attack #1, normal attack #1, slowed down normal atk #2 (that connects twice), special". Enemy based, as any other beat em up, meaning each time the move connects to the same enemy then the next one is the next on the combo. If it misses, then the combo resets. It would require a lot of room for new code and that's annoying to do when you're trying to keep compatibility with other hacks. And it would require understanding the 2 hit normal attack bug, which I couldn't.
The game has partial support for 4 enemies on the screen, but the fourth one will just run away and never attack. They probably decided to have max 3 instead of fixing that before release.