I don't recall us getting the explanation how he ended up that way.
I don't recall us getting the explanation how he ended up that way.
The Terrifics said that Batman and Mr. Terrific brought him into examine some of the Dark Multiverse stuff seeping into the world and it had an adverse effect on his physiology that trapped him in that egg form.
I'm pretty sure they explained in Metal that Plas was protecting himself because he had some connection to Barbatos and the noise of his impending arrival was becoming too much for him... so he retreated into an egg form ... or something.... Yeah, that whole series barely made sense...