Quote Originally Posted by Enkidoh View Post
There is no explanation lore-wise as far as I can tell about exactly how zombies are reanimated in FFXIV.
Time for some 1.0 Lore!
In Ul'dahn lore it is believed that those whose are left unburied outside the city walls will rise again as undead corpses. This was evident mainly by the skeletal wight roaming the wastes and a few zombies from levequests, although the wights seem to be devoid of thought.

I bet Dalamud's interference with the land's Aether has made this more powerful. Also there's the fact that the ruins of Sil'dih were partially uncovered, which was a City-state that fell from Necromancy gone bad and was sealed up by Ul'dah with a Zombie horde inside.

But no explanation as to why certain ones are more intelligent, nice touch though.