instead of going all out and creating an enemy editor that can allow totally new enemies, why not start with something small, like this;

OK, right now, if we want a new enemy, like, say you want to make a human archer along with the Red and Black moblins. right now, all we can do is change the graphic it uses, right? well, this editor would allow a new enemy, with pre-existing stats (HP, damage it deals, what weapon it shoots, ect...), only you can define what tiles it uses for the sprites. so, instead of having to change a moblin into the archer, you could create a new graphic for the archer and still keep the Red and Black moblins. you could also define what sprite pallete it uses (7-9, then the extra sprite palletes), and define the behavior (stalfos, moblin, leever, ect..)

so, instead of defining ALL aspects of the enemy, we just define that graphics and behavior. does this sound a little more do-able then a full scale editor?