Transforming Construct

[BigP4nda]

So after looking at intelligent items a bit, I saw the transforming power. I am trying to make an artificer-type wizard with a construct mount. A horse that transforms into a giant eagle.
I began to think about homebrewing a complex construct modification that allows two or more separate forms to transform into. Based on your experience with custom weapons, armor, items, etc. What do you think a good additional cost would be. Here is the explanation of the modification:

Transform
Requirements: Craft Construct, Craft Magic Arms and Armor,???
CR increase: +2 ???
Cost: ???
This modification allows the construct to transform into another form. This form must be the same size category as the construct and both forms must have the same CR (excluding the increase from this modification.) Each form is treated as its own separate being with its own stats and abilities except for its Constitution ability score. Any damage the construct takes is retained in both forms, consequently any damage recovered is also recovered in both forms.
All construct modifications (except this one) are separate and can only be used while the construct is in the corresponding form.
All skills and feats are preserved in each form. The construct does not gain the benefits of any feats unless it's current form has said feats, and the construct is considered trained only in the skills that its current form has ranks in.

Also I'd appreciate any constructive criticism in the description. Thank you!

[Ipslore the Red]

Mechanically, this doesn't seem like it should increase CR much by itself, with the CR limitation on the transformation. I'd be fine with it being a CR +0 template, maybe a CR +1 at most. There are a few under-CRed, overpowered enemies at most CR ratings, but that's a problem with those enemies, not the transform ability. Just having an unspecified alternative form isn't a huge deal.

Also, how exactly does the transformation work? Does it mimic undead anatomy X, beast shape X, plant shape X, and so on for one selected form? Does it give the construct the exact stats of the other creature, excluding the transformation ability and the Constitution score? The latter is probably not viable, since that was how polymorphing worked in 3.5e and it was horribly broken, necessitating the change in PF to how it is now.

I assume it's a standard action to transform?

[CrinosG]

There's actually a transforming construct template in Green Ronin's advanced bestiary, there is another version of the same template in Purple Duck Game's Monsters of Porphyra. (The first advanced bestiary was in 3.5 rules, and Monsters of Porphyra is all about updating monsters from old third party third edition books to Pathfinder).

For the Green Ronin version, the template increases CR by one per different form it can take.

[BigP4nda]

Forgot to mention the action used. Yes it would be standard though I may change it to full-round. As for the stats. They would be design the same way you would design a new construct using this guide. The type or shape of the form is up to the builder.

[Goth Guru]

Seems fine except Polymorph any Object is a requirement. If that seems excessively high level I suggest researching a polymorph only objects spell. At 5th level it reshapes an object without changing the material it is made of.

[BigP4nda]

It seems my original question was never answered. What would the additional cost be for this type of modification?

[CrinosG]

Well the Advanced Bestiary version, its 12,500 GP for this modification. So that could be a good baseline to estimate for your thing.

[BigP4nda]

CrinosG wrote:

Well the Advanced Bestiary version, its 12,500 GP for this modification. So that could be a good baseline to estimate for your thing.

Awesome thanks!