Big fuzzy 3 eyed bat thingies, the Tetraps were good friends with the Rani. When the 6th Doctor regenerated into the 7th Doctor, he had some brain poo going on where he became super confused and gullible. The Rani was able to convince him that she was his pal Mel so she could do bad guy stuff to the Doctor. The Tetraps were great spies (the whole 3 eyed thing) and were happy to do the Rani’s bidding while she was manipulating the fresh new Doctor. That is, until they found out that The Rani was a bad guy and was probably going to kill them all anyway with Rani experiments involving giant planet shattering asteroids. Then they kidnapped her and took her to a far away planet where they could enact kinds of revenge

They were seen in Time and The Rani.