Happy New Year everyone! As it turns out, we managed to find a Christmas-themed transformation after Christmas, so consider this a New Year's present. My thanks to two members of TF-Spot-- Vampgrey, who found the TF, and Werefan, who provided the video.
"Reindeer Games" is episode 4 of this Youtube red webseries. The plot involves a crook who runs over Rudolph the red nosed reindeer and starts gradually transforming into him. His mom almost stops this through a magical ceremony involving Rudolph's corpse, but in the end her son transforms completely. I've edited together bits from various parts of the episode to show the progress of his mutation--my apologies for the rough transitions. The budget was obviously low, so adjust your expectations--there's not much onscreen transformation and the final stage is done with shadows (alas). But it's still fun.