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

[yeetusmcgeetus]

I'm my group's forever DM, so I'm mostly asking out of curiosity.

[Inevitability]

Exalted Companion is the easiest way, lets you turn any normal animal companion into a celestial creature and thus a magical beast.

edit: also, Ghostwalk has a spell to raise an animal companion as a ghost iirc, and even with ghostwalk ghosts being a bit odd that's still a type change (though to outsider instead of undead)

[Morphic tide]

3.0 Masters of the Wild, IIRC, provides a procedure for keeping Awakened Animal Companions, though the mechanics are tied up in the Animal Friendship spell behind Ranger's slowed progression.

[MaxiDuRaritry]

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...

[ShurikVch]

Do you need to change the Type of existing Animal Companion - or just get creature of some unusual Type as a Companion?

[yeetusmcgeetus]

Do you need to change the Type of existing Animal Companion - or just get creature of some unusual Type as a Companion?

Either way. Just looking for ways for a druid to have a non-animal companion

[Inevitability]

Either way. Just looking for ways for a druid to have a non-animal companion

In that case, there's also:

Totem Companion (ECS)
Vermin Companion (ECS)
Blessed of Vulkoor (Secrets of Xen'Drik)
Spider Companion (DotU)
Elemental Companion ACF (Complete Mage)

[Biggus]

If you play up to epic levels, there's also Magical Beast Companion (ELH).

[ShurikVch]

Either way. Just looking for ways for a druid to have a non-animal companion

Feats:
Monstrous Animal Companion (Dragon #326): even at 4th level gives such options as Grick, Krenshar, Psedodragon, Shocker Lizard, Worg; 16th level would give access to Arrowhawk (elder), Behir, Gray render, Hydra (eight-headed); caveat - in order to get MAC, you must actually met the creature and either Charm Monster, or Wild Empathy it (prerequisite feat allow to use WE on a selected non-Animal type; but Construct, Humanoid, and Undead are off-limit)
Tainted Druid - this 3.0 feat allows Fiendish Animal Companion

Spells:
Planar Familiar - RAW explicitly mention "... animal companion ..."; the problem is - it's Cleric-only spell...

ACF:
Plant Companion (Dragon #357)
Urban Companion - allow creatures from the Familiar list as you Companion; no requirement for it to actually be an Animal - thus, all Aberrations(/Constructs/etc) are available

Alternate Classes:
Urban Druid (Dragon Compendium) - Urban Companion: mainly of Construct and Vermin types, but at 7th level list includes Carrion Crawler and Otyugh
Wind Walker (Dragon #311) - Companion must be a flying creature; higher-level options include hippogriff, giant eagle/giant owl/juvenile arrowhawk, griffon/adult arrowhawk, dragonne, and elder arrowhawk

PrC:
Vermin Keeper (Underdark) - Vermin Companion

Possible combo:
Urban Companion ACF or dip in Arcane Hierophant + 5 levels in Alienist = Pseudonatural Companion
Urban Companion ACF or dip in Arcane Hierophant + Animate Dead Familiar spell = Undead Companion
Urban Companion ACF or dip in Arcane Hierophant + Betrayal of the Spirit Linked feat (Dragon #336) - sacrifice your Companion-Familiar to animate it as a Skeleton or Zombie
Urban Companion ACF or dip in Arcane Hierophant + Construct Familiar feat (Dragon #280)
Urban Companion ACF or dip in Arcane Hierophant + Darkness Familiar feat (Dragon #322) - list includes several Magical Beasts, Undead, Small Elemental, and even Dark Creeper (i. e. Humanoid!)
Urban Companion ACF or dip in Arcane Hierophant + dip in Fleshwarper = Aberrant Companion
Urban Companion ACF or dip in Arcane Hierophant + Undead Familiar feat (Dragon #280)
Either Leadership feat or dip in Windrider PrC + Devoted Tracker fear = pretty much any rideable creature as a Companion (i. e. your Mount is also your Companion now)

[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.