Why are enemy locations so odd? For example, Eindons show up in a whole ton of locations. The only time they'll never really appear anyone is in Ayn's paths. Other enemies can be placed so randomly - such as enemies in G3 Western Cave or Shusoran.
Some enemies also appear in places you'd never really expect - Kensais and Dragons show up in G2 Dahlia Dungeon, and G3 Draconia being used as a disposal for nearly all remaining recolours. There are also a lot of enemies you'll never meet depending on your generation (though this is kinda forgiveable).
There's also the removed enemies (e.g Imp, Gryphon, Twistbot), but there a bit of a different story...