Anti-molecular ray disintegrator
From Tardis Wiki, the free Doctor Who reference
An anti-molecular ray disintegrator was, according to the Second Doctor, "a scientifically impossible weapon". The fictional superhero Karkus was armed with one.
While in the Land of Fiction, the Doctor and Zoe Heriot encountered the Karkus, who was armed with his ray disintegrator. Zoe warned the Doctor about it, but the Doctor said it was "scientifically impossible". The gun then disappeared.
The Karkus later used it to destroy the clockwork soldiers threatening Jamie McCrimmon and Zoe. (TV: The Mind Robber)
