Like the Santa Norns, there are two distinct breeds called the "Santa Grendels". Unlike the Santa Norns, they are both unofficial.
One was designed by Bean of ALB-Labs, and uses grendel breed slot 2.
The other "Christmas Grendel" (named, appropriately enough, 'Jingle') was designed by Slaterbait of The Mechan Saga, and he uses grendel breed slot 5.
One of the Santa Grendel breeds is available at MadDoc's Welt. Jingle is available at The Lost Archives.