At the end of Attack on Titan Season 2, the theory arose amongst the Scouts that titans were transformed humans, and this would later be confirmed in Season 3. Throughout the first two seasons there were clues to this, especially when Eren first transformed into the Attack Titan and when it was revealed Annie was another shifter; however, the biggest clue to this was with Ymir, a character who was a mystery from day one.
While other protagonists got some form of backstory, Ymir’s was always kept in the dark, and for good reason. It wasn’t until Season 2, Episode 4, “Soldier,” that it was revealed she was another shifter, and shortly after, in Episode 5, “Historia,” the audience learns she obtained this power by eating one of Bertholdt and Reiner’s comrades, which turned her from a mindless titan into the shifter known as the Jaw Titan, who was originally sent alongside the Titan Trio to destroy the walls and obtain the Founding Titan. Like all shifters, the Jaw Titan has a unique anatomy compared to mindless titans, which gives her an advantage
Upon first glance, the most notable thing about this shifter is her size. Compared to all the other shifters introduced in the anime – the Attack Titan, the Colossal Titan, the Armored Titan, the Beast Titan, the Cart Titan and the Female Titan – she is the smallest, and she is even smaller than most mindless titans. This comes with advantages, which will be addressed later on, and disadvantages, such as being overpowered by larger titans, as seen in “Historia” when the mindless titans finally outnumber her, toss her like a rag doll and devour pieces of Ymir.
Unlike the Colossal Titan or Rod Reiss’s Titan, who both move ungodly slow due to their massive sizes, the Jaw Titan, thanks to her petite build, is one of the fastest shifters. Throughout second half of Season 2, audiences see Ymir easily catch up to Reiner’s Armored Titan and out run the scouts with their ODM gear. Even before the other characters know about the Jaw Titan, Historia notices that Ymir is hiding something when she makes it down the mountain with Daz without any climbing gear and in record time. This should’ve taken an average person hours, and even for a titan it would’ve taken a while, but Ymir’s Jaw Titan speeds down fast enough to save Daz from hypothermia.
Along with heightened agility, the Jaw Titan has more flexibility and dexterity than any other shifter. While the Armored Titan, Female Titan and Attack Titan have all displayed fighting capabilities, they do not have the same grace as the Jaw Titan, who can easily maneuver out of tight situations while also landing devastating blows. At Castle Utgard, fans see how effortlessly she can scale the tower, leap from titan to titan and hurl pieces of brick at her opponents, mimicking the grace of dancer or spider. Meanwhile, in the Giant Forest, Ymir swings like a monkey from branch to branch and preformas flips like an acrobat, which allows her to escape the Scouts.
What helps with her acrobatics is her sharpened claws. While other shifters, like the Female Titan, have had to use their crystal abilities to make claws, the Jaw Titan naturally has a set of nails that can penetrate the hardest surfaces. With Castle Utgard, Ymir is able to hold onto a smooth surface thanks to her claws, and she is able pierce titan flesh with them, which is impressive when considering the fact that the Scouts had to develop specialized bladed to achieve the same feat. Similarly in the Giant Forest, Ymir can hang onto trees like the Scouts because her claws anchor her like their ODM gear does.
The biggest advantage of the Jaw Titan is her jaw, which is the strongest of the titan shifters. Where most shifters and mindless titans have teeth that resemble their human set, the Jaw Titan develops a mouth full of razor sharp fangs. Along with being sharp enough to easily penetrate the nape of titan’s neck, this jaw can unhinge itself without the need of damaging the mouth, as the Female Titan has had to do. This makes the Jaw Titan’s anatomy similar to that of a snake as well as an alligator given the immense amount of strength the Jaw Titan can exert in a single bite, which makes this shifter incredibly dangerous.
As one of the nine shifters, Ymir's Jaw Titan has a unique anatomy and in turn a unique set of skills in Attack on Titan.