RTF is a global modification that replaces all towns in the game.

neutral undead will be something like this – these are monsters created by the first necromancer. He wanted to create perfect servants (skeletons are too stupid), so he used magic to create cocoons-incubators from flesh. As a result, these monstrosities hatched from them. By the way, the flies are a random product of this experiment – some of the cocoons were made from already decaying corpses, and larvae ended up inside, developing into giant flies.