Its a minor (or major if you plan to do damage from the transformation) transformation attack, but it gets very expensive very fast depending on modifiers. To be a true "Gravity Hero" you almost have to put it in a VPP with the limitation of gravity powers only. This lets you use Tk, Flight with usable on others and uncontrollable, and transform attacks. At least that's how I built my guy. He's fun to play, but it usually takes a couple of phases to transform someone (especially if they have any power defense). However, you will own perps that use foci. When you make Binders gun weigh 10 tons...he is kinda screwed..8)...
I had a player try to use density increase usable on others with the limitations of only applies extra weight and kb res, but this was kind of a stretch. Plus it was really powerful for pretty cheap. But if that would work in your campaign more "Power" to you.
Sorry to repost..it timed out on me the first time.