A fighting drone was a piece of technology owned by Strax. It produced a hard light hologram that took the form of the person it locked onto and if it perceived someone as a threat it would fight that person to the death.
In 1894 Strax secretly tinkered with his fighting drone. The drone malfunctioned and began roaming Paternoster Row, making the residents believe a ghost was haunting them. The drone eventually locked onto Jenny Flint and took her form with a holographic katana, but before the drone could kill Jenny its battery died. Madame Vastra banned Strax from operating his fighting drone on earth anymore. (PROSE: The Spectre of Paternoster Row)