Board Thread:The Panopticon/@comment-4028641-20151008023030/@comment-6032121-20191111140232

He loses his Trakenite body, turning back into Beevers, then uses regeneration energy stolen from the Doctor via a complicated process to properly regenerate into a body identical to Tremas's form, which he's gotten pretty used to.

Also, I of course get what you mean, but please try to use more precise terminology for how the Master gets bodies, this is all confusing enough as it is. Even if the Doctor calling Beevers->Ainley a "regeneration" doesn't convince you, it's not shapeshifting, but body-hopping. Shapeshifting, in fact, means precisely the opposite of what you mean: it's usually employed to mean warping the shape of one's body around, precisely as opposed to transmigrating from one physical body to another. It's not usually described in those terms but regular Time Lord regeneration is shapeshifting.