Since I have ideas for this, I will elaborate for you.
Deers would have a 2x2 hitbox.
Deers would have 20 health (10 hearts)
Deers would be neutral creatures, which like polar bears, will attack if a nearby baby is.
The main difference between deers and llamas is that deers will have a melee ram attack, where the deer will charge forward at the speed of a baby zombie, dealing 2.5 hearts of damage and removing aggravation.
Deer would spawn in the Taiga and Mega Taiga variants, in packs of either 2 (1 adult and 1 baby) or 3 (3 adults).
Deers would be bred using golden carrots.
Deers would drop 0-2 leather (like the other "horse-like" creatures in the game) and on rare occasion, about 1 in 100 kills, will drop a "Deer Hat", which would be a deer head which would rest in the helmet slot, which would look alot like Randolph the Blood-Nosed Caribou from Team Fortress 2 (https://wiki.teamfortress.com/wiki/Randolph_the_Blood-Nosed_Caribou) but blockier, of course.
The Deer Hat could be "infused" with a helmet in a crafting table, to give it the properties of it (enchantments and armour points).
During the Christmas event, the nose of the deer will become bright red, as a reference to "Rudolph the Red Nosed Reindeer"
To be fair, you have to have a very high IQ to understand KittyCatPerson's threads. The humor is extremely subtle, and without a solid grasp of theoretical physics most of the jokes will go over a typical viewer's head. There's also KittyCatPerson's nihilistic outlook, which is deftly woven into his characterisation - his personal philosophy draws heavily from Narodnaya Volya literature, for instance. The fans understand this stuff; they have the intellectual capacity to truly appreciate the depths of these jokes, to realize that they're not just funny- they say something deep about LIFE. As a consequence people who dislike KittyCatPerson's threads truly ARE idiots- of course they wouldn't appreciate, for instance, the humour in KittyCatPerson's existential catchphrase "spank me daddy," which itself is a cryptic reference to Turgenev's Russian epic Fathers and Sons.