
Dreaming Psion |

Another idea for a unlikely lich:
Nature's Wrath: a blight druid driven by bitterness at losing his grove and everything else he holds dear, now plays a war of "scorched earth" tactics against those who ruined his home. He has sworn eternal vengeance. (Formerly a normal druid but retrained his levels.)

pennywit |
I researched the requirements for the Five Flames General, above. After looking to clockworks, I realized a magus wouldn't work, given the spells he'd need to construct the clockworks wouldn't come until he's much, much higher level than what you want. Tentatively, I would therefore build him as a wizard/fighter/eldritch knight.

Dreaming Psion |

Now that I think about it, a dragon disciple could be a subordinate to the lich, rather than the lich itself. Sort of a penultimate baddie to make the final battle that much harder.
In Ravenloft, they had the concept of the "vassallich" a vastly lesser powered version of a lich bound to a lich's service. They lost they ability to gain levels/experience, but the lich lord they were bound to could grant XP to them at his whim. Might make for an interesting option if you wanted to make a dragon disciple subordinate.