I'll have to give Haunt Shift a read-through. Sounds interesting. Also, will it register as undead with stuff like Detect Undead? It's a bit of a campaign issue.
Edit:
Looking at Haunt Shift (for 12th level): how do you control the object? It says it can't be rebuked.
It takes a lot of work to figure it out.
First of all, you rebuke it BEFORE you haunt shift it into the new object. This means the controlling essence is yours (remember, in D&D effects stay on a target even if the target changes to later being invalid). It's probably not going to detect under Detect Undead, considering it defaults to the rules for Animate Object (which is actually a construct). It has 60ft of vision and no more, though other abilities might help it detect at longer range (for example, putting a Bone Creature Beguiler/Mindbender with Mindsight into a haunting). It has the mental scores of the undead, but the physical stats of an Animated Object of the appropriate size, and has the hardness of such an object (making Dwarvencraft Quality Obdurium critters extremely durable).
Anyway, it takes a lot of work to figure out what all Haunt Shift does, but it's amazing once you figure it out. Especially consider making bodies for the purpose... remember that extra legs give more speed, wing like surfaces let them blind enemies while grappling, etc. Also remember that the body is an object before you cast Haunt Shift, so certain long duration spells are worth casting... Invisibility can be made permanent on an object (though attacking would still break it) and Shrink Item on a Huge object turns it Tiny, so with Permanent Shrink Item you can have something that swaps from battle form to concealable form.
My favorite battle form to give a minion is a Huge statue that looks like a claw footed centaur with four arms and giant wings. The wings don't let it fly, but they do blind enemies in grapples, and nothing stops the critter from using all those arms. The clawed feat is mostly just so it makes sense to have the thing climb about.
JaronK