What is an item that allows the user to become incorporeal?

[Mulet]

I have a human NPC I wish to use a boss. I want her to be able to become incorporeal at will for a round or ten.

What item/s can do this?

Bonus: If it could be activated as an immediate action, that would be amazing.

[Claxon]

Scroll of Ethereal Jaunt. It will last for 13 rounds. It would be very expensive though, and would require UMD to use unless you had a sufficiently high level wizard or cleric.

[avr]

It costs the Earth, but a shadowform belt is more or less what you're after.

[Mulet]

avr wrote:

It costs the Earth, but a shadowform belt is more or less what you're after.

Oh dear lawd, my question was answered within seconds. Praise avr!

Claxon wrote:

Scroll of Ethereal Jaunt.

I did not consider Ethereal for an equitable effect. Brilliant.

[Fourshadow]

http://www.archivesofnethys.com/MagicWondrousDisplay.aspx?FinalName=Spectra l%20Shroud

Another item, still a little pricey at 26K.

Spoiler:

Spectral Shroud
Source Ultimate Equipment pg. 222 (Amazon)
Aura moderate necromancy; CL 5th
Slot chest; Price 26,000 gp; Weight —
Description
This thin, bleached cloth covers the wearer’s entire torso. Some also cover the wearer’s face, but don’t interfere with the wearer’s vision. The morbid burial shroud grants the wearer some affinity with the spectral dead. The wearer can discern invisible or ethereal creatures as though using see invisibility. Once per day, the wearer can become incorporeal for 10 rounds and gain a fly speed equal to half his base speed with perfect maneuverability. The wearer can’t attack while incorporeal, but can dismiss the effect as a move action.
Construction
Requirements Craft Wondrous Item, hide from undead, see invisibility; Cost 13,000 gp