This is a tool-assisted speedrun. For more information, see http://tasvideos.org/4079M.html. TAS originally published on 2019-12-10.
X-COM: UFO Defense is a revolutionary turn-based strategy game in which the player is given the role of the commander of humanity's last hope against the alien invasion. However, this alien menace must not only be fought with bravery and tactics on the battlefield, but also with study of captured alien technology and maintenance of a proper budget.
This TAS by willbobsled manages to beat the game in under 15 minutes by only partaking in 3 missions and with careful planning and luck manipulation.
You can read the author's commentary in the YouTube stream by enabling closed captions.