Joy to the world, the tests are run! The result is a spectacular three-minute Portal carol built in Source Filmmaker by Harry 'Harry101UK' Callaghan. The turrets—including the Animal King, naturally—have come together at this special time of year to spread neurotoxin to the tune of Mykola Leontovych and Peter J. Wilhousky's Carol of the Bells.
Callaghan did the voices and music himself, with turret rigs provided by August 'Rantis' Loolam, which is an exhausting array of talent and an indictment of my own sorry skillset. You can find his YouTube channel here, and the song is available on Bandcamp.