This article might have further canon details available on.
In their natural form, reptoids are gaunt humanoids with scaly skin, a weak nose, a tail, and a wide, lipless mouth filled with sharp teeth.1
Reptoids can assume the appearance of an individual humanoid of appropriate size. A reptoid can select a new humanoid form by spending a week preparing for the change, but can then no longer assume the previous form.1
Reptoids never reveal their homeworld to others, even under duress. Disguised as other races, reptoids seek positions of power in order to secretly prepare for an invasion. Reptoids are adept at psychic magic, which they use to cover their deceptions and to ensure the complacency or collusion of others, and even those aware of reptoids in their midst can never be sure who is actually one.1