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

Yeah, I split them up because I ran out of ideas – a separate winged one, a separate fiery one.

Added 16 hours 17 minutes ago

From folklore, only "yeratnik" – a sorcerer risen from the dead – fits the meaning.
In principle, you could use the name "demilich," although in D&D, these are flying skulls, but the point is that a demilich is more powerful than a regular lich.
Or you could create a word-homunculus from two names you like, or play around with Latin, but that's a very popular language.

Plus, the "arch-lich" and "demilich" constructions, due to their length, are easy to read. You could drop the "lich" ending and call it something like "damnari" (from the word "damnare" – cursed), "mortumanti" (mortuum – dead in Latin), or "infirmant" (from the word "sick"), although that sounds a bit strange. These are more like names for regions; "Damnaric sorcerers" sounds better.

Added 12 minutes ago
Here's another point: since this isn't a lich, but a sorcerer who has risen against his will, he could call himself a sorcerer/wizard, or it could be an ancient word in his native language.