Any way to change the creature type of a druid animal companion?

[Nikorasuko]

Polymorph?

Also, there's a changeling wizard ACF where you can change your familiar into any other familiar you have at your potential disposal. Use arcane heirophant (I think that's the one) to combine your familiar with your animal companion, and...

Then the animal companion can benefit from Familiar feats that allow you to apply a template onto your animal. Hello shadow companion.

Morphing the animal between multiple templates is actually awesome.