Morphic illusion

Morphic illusion was used by the human-form Krillitane, Brother Lassar, as a description of how his bat-form brothers assumed the appearance of humans. (TV: School Reunion)

Historians who had been allowed access to the "Monster Vaults" of the databanks in the Doctor's TARDIS claimed that Abzorbaloffs concealed their appearance using a type of morphic illusion like the Krillitanes. (PROSE: The Monster Vault) Indeed, one Abzorbaloff adopted the human form of Victor Kennedy, (TV: Love & Monsters) giving off a green glow when he returned to his true form. (WC: Tardisode 10)