BBEG for campaign, swarm question

[EgyptFanatic]

I was wondering if there was anyway besides Spherewalker to turn into a swarm for my Osirian big bad who is meant to be the end boss in my little campaign.

Sample Version:

Aasimar (Native Outsider and Human)
sorcerer 15 (dual blooded, Stormborn and Undead) / Spherewalker 5.

STR: 7
DEX: 18
CON: 12
INT: 10
WIS: 13
CHA: 20

Traits: Freed Slave (+1 to Will saves), Deft Dodger (+1 Reflex Saves)
Feats: Improved Unarmed Strike, Deflect Arrows, Snatch Arrows, Iron Will
Special gear: Ring of Evasion.

Note to Self: Change the fluff from swarm of butterflies to swarm of scarabs

The reason why the sample version is so sparse is I don't want to give everything away in case a player stumbles upon this.

[meowstef]

something like
http://paizo.com/PRD/additionalMonsters/wormThatWalks.html ?

has the template down the bottom

[EgyptFanatic]

OH GOODY! That will work just perfectly. Thank you very much meowstef.
:)

EDIT: Yes the build may seem cruel, but to be fair I have warned my players more than once that I don't pull my punches and the final fight will be an uphill battle.