Voluntary Shapeshifting: In a variety of limited forms. There are clades which possess a limited ability to change shape within the general parameters of their species (shifters); which are designed to shift between multiple shapes, usually two, although limitations on this and parts reuse tend to make neither shape look exactly like what it’s imitating, if it is (weremorphs – you can build a werewolf this way, if you can live with the were being somewhat wolfy and the wolf somewhat were-y); which possess the ability to shift sexes within their basic parameters (hermaphromorphs); or which are essentially blobs of nanoglop which can adopt any shape they feel like, with the caveat that the nanoglop can’t magic itself up additional organ functions, change mass or volume (damn you, physics!), or look even remotely like what it’s imitating internally, albeit this is still incredibly flexible (polymorphs).

In practice, body-switching is much easier and more flexible when you want to adopt a different shape for more than the briefest periods.