@Qube: really f***king interesting!! Too bad I did not see that earlier. I thought that the Bros were very secretive about their code/dev methods. If only we could get hold of those tools!!!
CRIPAL must be the name of the system. I saw that in a PC data file.
Funny thing is if you use my editor you'll find that I've done a very similar system, with associations, etc... My editor is graphically more powerful but some complex stuff is script (Java) based to avoid developping a language that was too complex.
When you check the screens, you see indexes and x,y coords, so you have to input them manually. It was 1989 at the time, so it was great, but they must have had a hard time inputting all the game data!
I think that their system still generated asm code and the game did not embark the engine itself (I saw self modifying code such as NOP becoming RTS when spikes are killed).
Also, I used a smart technique to define what is a platform. I avoided the extra mask layer by tagging each platform tile as "platform", but allowing exceptions. It saved the tedious task of double editing the gamemaps.
The intelligent alien editor part was really very interesting for me. Seems that I missed some stuff such as "avoid shots" for walking monsters (I coded it only for flying monsters).