[simulatoralive]

Okay, here's my current way of thinking:
Fragile (Unnatural), so it dies at a consistent point, every time.

Add a limitation to ST such that it scales according to HP. Not sure what the value of this should be.

Add a limitation to part of Basic Speed such that it's inversely proportional to HP. Not sure what the value of this should be, either.

The size changing bit can be a zero point feature, with perhaps a perk that allows it to shed HP in order to get smaller.

Finally, it has Regeneration with a limitation that it can only heal by absorbing the proper materials (re-absorbing the mass that was knocked off it in battle is allowed). In addition, it has Unhealing (Total) to represent that it cannot heal without using the Regeneration ability.

So, I need to figure out limitation values for ST, Basic Speed and Regeneration.

Edit: After reading Peter Knutsen's post, I'm thinking ST and Basic Speed will be tiered like suggested.