Matter condensation

Matter condensation was a technique used to shrink inorganic or organic matter.

The Master picked up the technique "somewhere on his travels", according to the Fourth Doctor, and employed it with murderous outcomes, such as against a cameraman on Gallifrey. (TV: The Deadly Assassin)

It could be performed on humanoids, under the rays of a dimensional stabiliser from a TARDIS, without causing harm. (TV: The Invisible Enemy, The Armageddon Factor)

In 1966, the faceless Chameleons miniaturised and stored young Earthlings from all over Europe; their purpose was to steal their identities, lost after a catastrophe on their planet. (TV: The Faceless Ones)

During the 57th Segment of Time, on the Ark, most of the Earth population, fleeing from their home, had undergone a process of miniaturisation and been placed in suspended animation in order to face a 700 years journey towards Refusis II. A Minifier was the instrument geared for this purpose. Miniaturisation was administered as a sanction too. (TV: The Ark)