One of my favorite BBEGs (despite the campaign dying before much came to light of him that the PCs would have learned) was a custom monster type that was kind of lich-like. But instead of having a Phylactary, it was the caster becomes a sort of undead cloud of breath, sort of like how vampires become Gaseous upon their 'death'. It could either slip into a living thing and shred it like a Belker, or animate corpses, toughening them up to become its new host, taking on his mind and abilities while allowing him to use the body.
He also had a Minor Artifact that was a staff allowing him to cast a spell and create a Living Spell that he could sense through and telepathically command within the spell's range... his favorite spell for this? A Fell Animate Cloudkill. Oh yes. He was a fun little necromancer.
The final fight was planned to be against his 'favored' "Orc Form" ... and once it was crushed fairly easily, the 'Geistwolke' would exhale from that form and drift into an undead Hydra, becoming a Hydra with the mind of, mental scores of, and class features of a gestalt Dread Necromancer / Swordsage. It would have been epic. : (
The actual mechanics of the template were a trainwreck, but I loved the concept so much. <3
