Whifferdill

The Whifferdills are a species of sapient shapeshifters from the planet Xenon, which can morph into any form they wish to. Their natural form is that of pale-yellow humanoids with round featureless heads.

They are susceptible to a disease called mono-morphia, which causes them to be stuck on their current form, unable to change. Whifferdills are also a critically endangered species, with only about 15 individuals left.