Finally, I am still working on the Iron Heroes in Asgard adventure. Since I want it to be very memorable, I am taking my time and stealing only the best ideas.
What did I steal to prompt this post? The rock boss from Metroid Prime. You encounter it in the Phendrana Drifts right before you get the Spider Ball enhancement. I have not thought about stats yet (the Metroid boss has weak points that can only be seen with the infrared visor and, once breached with the charge beam, are destroyed with missile blasts) but obviously the thing is going to be big, strong, and tough as giant boulders of ice. I look forward to seeing what players think up when confronted with a disjoined series of floating boulders of ice orbiting an unseen, perhaps inconsequential point (i.e. no nexus of energy or brain or other vulnerable centralized command point in the midst of it all; it is just a point in space the rocks spin around).
Storms of razor ice and thrown boulders are obvious attacks, as are a pair of devastatingly powerful slam attacks (one of the rocks making up the creature's arm flies out and crashes into the victim or crushes him against the wall or the ground).
This makes me wish I had nicely painted miniatures.