Kasaavin

The Kasaavin were beings that could phase through walls, even those of the Doctor's TARDIS. They resembled a white shining humanoid, while allied with, but explained to the Thirteenth Doctor that this was because the human shape "amuse[d them]". When they emerged through a surface, they temporarily took the image of that which they had passed through.

The Kasaavin planned to "take" the Doctor's universe. They, along with Daniel Barton, were unknowingly part of the Master's plan to destroy humanity and rain destruction across the universe. However, this plan was ultimately foiled by the Doctor and her companions.

The Kasaavin were capable of transporting beings on Earth to the their native realm. They did this to the Master as revenge for him using them for his own motives. (TV: Spyfall)

Behind the scenes

 * The Kasaavin were voiced by Struan Rodger