Doctor Who: 10 Villains The Doctor Couldn't Defeat
6. The Pting (The Tsuranga Conundrum)
Even though it looks all tiny and cute, the Pting might be one of the most powerful foes the Doctor has ever encountered.
The Thirteenth Doctor had a run-in with this hungry little monster in Series 11's The Tsuranga Conundrum, where it boarded the Tsuranga spacecraft and proceeded to devour anything it could get its hands on - including parts of the ship.
And that's basically all the Pting wants to do: eat, and because it likes to munch on non-organic matter, there's almost nothing that can be done to stop it or contain it. Lock it in a cage? It will eat the cage. Put it next to a bomb? It will eat the bomb.
Oh, and as if this creature wasn't powerful enough already, the episode makes a point of explaining that it's impossible to wound or kill, and that its skin is toxic to most other life forms. The Pting is deadly, aggressive, and pretty much unstoppable.
So when the Doctor feeds it with an explosion and then ejects it out into space at the end of the episode, she hasn't really "defeated" it - she's just sated its appetite for a while and left it to go and chomp on somebody else's spaceship.
Considering the Pting's abilities, that's really the best she could do.