Arkrhyst

At the end of the last session of my playtest game, the PCs woke the elder white dragon Arkrhyst from his slumber, and he barreled down at them from Rimeskull.

At this point in the campaign, the PCs are 17th level. It is ideal, then, that an Elder White Dragon is a level 17 solo brute. I don't think a single white dragon makes for a particularly interesting fight, so I'm planning on spicing it up with a couple of the new living spells released in this month's Dragon - it seems reasonable to rule that the presence of a portal to one of the most magically potent locations in existence might give rise to some stray magical anomalies. In fact, I like the idea that Arkrhyst's substantial time spent here has given him a few extra abilities - specifically the power to create and control a couple of these living spells.

I also want to drop Arkrhyst's hit points down to Monster Manual 2 standards, and give him a couple more abilities to even things out. First, to help with his damage output, I'll give him something to break through some of the PCs' cold resistance, especially when bloodied. PCs should be rewarded for having powers that supply them with the appropriate resistances, but in a fight like this featuring so much cold damage it can easily become an "I win" button.

So here are a couple questions that I'd love to hear interesting answers to:

• How should the Stone Runelord Heads feature in this fight? Should they be little more than terrain, or should they have a fantastical power that can be taken advantage of in the fight? Should they explode if caught in the crossfire of the battle with Arkrhyst?
• What other power or ability should I grant Arkrhyst, in addition to being able to reduce resistances? Should he have something that lets him command living spells actively? Something else that highlights his arcane strengths?

Comment quickly!