Once he appears aboard his tiny orbiting bolt hole of a ship, he smiles, and pushes the smaller of two blinking red buttons near the control console.
Somewhere on board, a slide hatch retracts, and a flood of tiny metal spheres similar to edible ball bearings floods out, like the powdery spray of eggs from a sea sponge.
“Oh, and here you, go, have a cloud of proximity-detonated chronotic scatter mines…” he muses, as he pushes the ship to planet comm, then reaches to tease the larger red button with his finger before bringing his fingertip up high above it and hanging it there, to amuse himself, “… and of course, because they’re time-active, these little Barcelonans will block all time-space signals coming to and from the planet. Ever. Which means no time travel off-planet. You’re all going to starve. Goodbye. I won’t be staying.”
Down goes the finger, and then…
His lightweight, single-passenger ship comes apart to the sound of his cackling, in a collection of loud, fluid bursts like a cooling lava rock, trailing a surprise symphony of nasty little puffball choruses above Gallifreyan space.
One by one, the lights of the Citadel go out as sensors black and monitors flush with static.