4e final boss

[The Dolman]

I'm thinking about creating a one shot at fairly high levels that culminates with a fight with an insanely difficult solo. I know solos have balance issues in 4e, so if anyone has any advice on how to avoid making a bad monster, it would be appreciated.
I've brainstormed a few concepts for making the monster unique, and interesting tactically. Please tell me which ones you think would work best.

Areas that summon relatively weak, but annoying reinforcements (Possibly with a fairly difficult deactivation sequence)
More than one turn per round
Nonstandard hitbox
Multiple phases (in addition to bloodied, nonbloodied)
Uses corpses of defeated players against his enemies
Periods of inactivity, or stasis, after a nova
Immunity to a random status effect each round
Additional saving throws
Extra action points triggered when bloodied
Aura
Healing (possibly regen, with some way of disabling it)

Also, should I add hazards and traps, or terrain suited to the boss?

[Composer99]

Multiple phases (in addition to bloodied, nonbloodied)

As I recall, the D&D blogger who goes by the "blogonym" The Angry DM posted a long article about adding just such steps into "boss fights" in 4E. It seemed like a pretty cool idea since it was a way to keep the fights from becoming static slugfests and required the players be prepared to adopt new tactics and adapt to changing circumstances.

Edit: Here is a link (http://angrydm.com/category/features/the-boss-fight/) to his series of posts on the subject.