The Deepest Cover - Has it been found?

[Phhase]

So I've been wondering, and maybe it's been done before: How deep undercover can you go in 3.5? So to speak, without duplicating an effect, how many layers of shapeshifting and alternative identity can you hide beneath? How big can the matroshka doll get? Is this something that's been done?

[icefractal]

For a literal matroshka doll effect, you can be inside at a series of creatures as long as you have control over all of them. Although more than two layers poses some logistical issues.

Example with three layers:
1) Cast Magic Jar, and possess a minion ("Middle").
2) In the body of Middle, PAO your original body ("Inner") into a marble (made of bone if you want a higher duration factor), and have Middle swallow it.
3) Make sure that Middle doesn't need to breathe or eat, and has protection against acid and bludgeoning, via items/buffs if necessary.
4) Go back into the jar, and possess a minion large enough to swallow Middle whole ("Outer"), which will then do so.
5) Middle readies to swallow the Magic Jar gem if Outer is destroyed, at which point you re-possess Middle and continue from there.

You could do this with more than three layers if you can find enough suitable minions, although I'd assume you're going down by at least a size category each time so there's a limit.

You can also store "assist" minions at various layers, polymorphed into a small stomach-proof form, who can cast buffs/healing on the layer they're inside. Confuse foes with how you're apparently casting multiple spells/round. You can store additional backup bodies this way as well, though deploying them will requiring dispelling PAO so not automatic.

This is more of a defensive strategy than a stealth one, but it does have the advantage that people can't see your true form, regardless of True Seeing or the like, because they don't even have line of sight or effect to the real you.

Note: There's a major limitation with more than two layers - you don't have LoE to all of "you" at once, so trying to Teleport is going to leave parts of you behind. You'll need to use continuous transmission methods like Gate.

[Thurbane]

I believe a Ghost could use Malevolence to possess a corporeal Fiend of Poesession; the FoP could then possess a Yakfolk, who in turn could possess the body of a giant or humanoid.

[Telonius]

I believe a Ghost could use Malevolence to possess a corporeal Fiend of Poesession; the FoP could then possess a Yakfolk, who in turn could possess the body of a giant or humanoid.

The humanoid could have originally been a Changeling with the Spymaster prestige class, that later became a Dragonborn of Bahamut.