A potent mental imaging fabrication apparatus devised by the Kree. Utilized by the duplicitous Yon-Rogg in his attempts to circumvent his hated rival Captain Marvel, it is a gadget that possesses vast matter & energy shaping applications. Enabling whosoever possessed it to conjure up and materialize anything ever devised by various Sciences.
When the Magnetron's rays hit its recipient user, it would create just about anything and everything they could possibly come to think of. Exposure to radiation from the Universal Power Core which energized it also had the effect of alternating the genetic structure of those using it, often giving them random but impressive post-human capabilities. To prevent random biophysical mutation by this highly radioactive Power Unit, the Kree contained it within a small shielded box.
Otherwise, once outside of it, the power core immediately changed its form to that of a much bigger, starred polyhedron. Emitting and blanketing everything around it in much larger quantities of the same radiation emitted by the main device itself when it bathed a subject user.
Radioactivity which if left unchecked, would burn, blind, and totally annihilate the senses instantly and, sometimes, even kill the subject in a few minutes. The radiation covered all known spectra and was strong enough to transform an area as wide as, say, Northern Florida, into a nuclear wasteland. Yon-Rogg somehow survived full exposure to this irradiation and gained even greater matter-shaping powers than the equipment itself.