The gnome-as-thrall setup is hilarious, but we'll have to run it past his DM. Technically, Savage Species
is 3.0, and I know that some DMs don't like allowing Leadership or Thrallherd. Plus, it will confuse his starting level--the imaginary bear can't actually have Leadership or Thrallherd by level five, and the gnome would have to be two levels lower than the bear. Assuming that the DM requires that the level cap apply to the bear "character," that could mean that the illusionist is a few levels behind the rest of the party.
Unfortunately, the symbiotic bear+pixie is technically rules-illegal, since pixies aren't valid candidates for symbiotic creature.
The ghost savage progression doesn't actually mention any specific creature types, but--going by the ghost template--the anthropomorphic bear would qualify, as it is a monstrous humanoid.
Thus, our possibilities thus far are:
- Bear is "imaginary," but is occasionally real. Invisible Spell + Summon Monster.
- Has imaginary bear that is entirely imaginary...but eventually becomes real. Animal Companion + Ring of Invisibility.
- Serves the will of his imaginary lord and master, Bear von Bearington. Invisible/Ethereal/Ghostly Bear/Bear-like-creature + Leadership/Thrallherd.
Any others?