Winter Veil event is here, and you've seen them scurrying around, getting underfoot everywhere - Elf Santas!
Now, to you Alliance folk who regularly have Gnomes running around, this is nothing spectacular, and a resourceful Gnome could probably find a near-complete Santa suit to dress up like an Elf Santa all year long, but us Horde folk need to revel in the one time of year that we can run around and be smaller than a Peacebloom.
How To Become An Elf Santa
Near the Zeppelin outside of either Orgrimmar or Undercity, there's a bright, glowing Gnome Engineer teleporter station that seems to be emitting a small snow squall of it's own, right there onto the non-snowy ground.
Run up on the pad, and you'll be TRANSMOGRIFIED into either a Green Elf Santa or a Red Elf Santa at random.
How To Become A Red Elf Santa
Follow the instructions above. If you are turned into a Green Elf Santa, run off of the pad and back onto the pad and it'll re-buff you with the Santa buff, again choosing either Red or Green at random.
If you stay Green when you hit the pad, back up and try again, knowing that the game had changed you into a Green Elf Santa again that time.
Keep trying until you're a Red Elf Santa (or Green Elf Santa if that's the one YOU really want to be).