So while I was endlessly fantasizing about a world in which my idea for a Christmas archetype came true, I realized one devastating point - if all of the monsters are constantly leveling up to any random level in the hopes of making them unique, then why on earth did I choose 10 instead of 12??? Christmas obviously happens in the 12th month of the year after all, and on second thought it might be a better idea not to give a deck the power to look at Gustav Max as a piece of cake. So from now on, let's consider all of the Reindeer as changing to Level 12 instead of 10.
Now, for the deck to really be appealing there's obviously gotta be some more Rank 12 monsters other than just (a newly rewritten) Santa Claus. I checked Dueling Network, and in real life not a single Rank 12 monster even exists. Ouch. So here's the goal for today - create a Rank 12 that will make this deck more appealing, while obviously trying desperately to avoid making it too broken. Let's do this.
Divine Charioteer of Zera
Light / Rank 12 / Fairy / 4000 / 2000
2 Level 12 monsters
You can banish two "Zera" cards with different names from your Graveyard; Special Summon this card from your Extra Deck. Any battle damage this card inflicts to your opponent is halved. Once per turn, during either player's turn, if a card or effect is activated that would remove this card from the field: You can detach 1 Xyz Material from this card and pay 500 Life Points; negate the activation and banish that card. Each player can only use this effect of "Divine Charioteer of Zera" up to three times per Duel.
So obviously this idea is related to the storyline of Warrior of Zera. Obviously I'm not an expert on that story and I didn't write it (nor am I even sure that there's a place where you can go read it), but I envision this as kind of being the final stage of his journey, assuming that he chose the path of light. Zera-focused decks obviously can turbo this 4000 beatstick onto the field which boosts their nearly invisible playability, but the real power comes from legitimately overlaying for this guy. It's a little bit like Felgrand, in that it's a big monster with a lot of protection. But unlike Felgrand, I decided to limit his effect's usage to prevent spamming, since ideally the Reindeer would be able to summon this thing pretty often.