Attack on Titan started with a relatively simple premise that eventually expanded immensely. Humanity lives inside the walls to protect itself from humanoid monsters known as Titans. Most Titans are Pure Titans, but there are Abnormal Titans, as well as Titan Shifters, who're the rarest. While each type of Titan shares similarities, like their origin, Abnormals and Shifters differ greatly from Prue Titans in a few areas.
What Are Pure Titans?
Titans are Eldians who've been transformed into monsters by having Titan serum injected into their systems. When they transform, their bodies turn into oversized caricatures of their former selves, developing over-exaggerated facial features and disproportionate anatomy. Their heights vary, with some smaller ones being around 16 feet, while some taller ones can be around 50 feet; however, this differs per Titan, and when it comes to Abnormals, the heights can be more extreme.
Along with this, if the victim turns into a Pure Titan, which is most often the case, they will lose all sense of humanity and intelligence. Their only motive is to search for humans to eat; however, this isn't because they need to consume people to survive.
All Titans, including Pure Titans, are durable, being able to regenerate from almost any injury; however, if the nape of their neck is severed, they will die. This leads to many Pure Titans throwing themselves into situations that could injure them greatly, but with their healing factor, as well as many of them not comprehending pain, this doesn't phase them.
Furthermore, they do not age, as seen with Ymir, who wandered Paradis as a Titan for about 60 years before eating Marcel Galliard, the former Jaw Titan. When she awoke, she looked the same as she did before her initial transformation. This, their regenerative ability, and the fact they don't need to eat to survive makes Pure Titans, as well as the Abnormal Titans, nearly immortal.
What Are Abnormal Titans?
Abnormal Titans abide by many of the same rules as Pure Titans, with a few differences, including their unpredictable behavior when it comes to hunting. While Pure Titans go after any nearby human, Abnormals will sometimes ignore certain people, often in favor of larger groups.
Some Abnormals -- not all -- also have larger or more impractical proportions, as seen with Rod Reiss' Titan, which was twice the size of the Colossal Titan, and he couldn't walk upright because of this. Similarly, Connie's mom, who Zeke turned into an Abnormal, is trapped on her back because her torso is too large while her limbs are too small.
These Titans' movements are also more varied, with some running or leaping on all fours, like the Titan who ate Thomas Wagner in the Battle of Trost District. Abnormal Titans also move faster at times and can have better dexterity, as seen with the Titan who killed Levi Ackerman's childhood friends in his OVA, "A Choice with No Regrets."
Furthermore, they appear to be more cognitive. For instance, one Abnormal lies underneath the trees while Pure Titans fail to climb up and get Reiner, Ymir, Bertholdt and Eren in Season 3, Episode 9, "Opening." Instead of repeating the Prue Titans' mistakes, this Abnormal keeps itself safe, watches its prey and waits for an opening, proving it has the ability to think and restrain itself.
In even fewer cases, some Abnormals retain memories and the ability to speak, like with Connie's mom, who tells her son, "welcome home." The Abnormal who kills Ilse Langnar also talks and even expresses remorse as Ilse interrogates it, showcasing how some Abnormals retain bits of their emotions, but their Titan instincts often overcome these more human qualities.
What Are Titan Shifters?
While Abnormals have some advantages, what they can do is nothing compared to what Shifters are capable of. A Shifter starts off as a Pure Titan; however, after consuming a current Shifter, they will inherit that person's Titan. As a Shifter, the person can change between their human and Titan form, and they do not have a desire to eat other humans.
There are nine Shifters in total: the Founding Titan, the Female Titan, the Beast Titan, the War Hammer Titan, the Armored Titan, the Cart Titan, the Jaw Titan, the Attack Titan and the Colossal Titan. At the start of the anime, all of these Titans, aside from the Founding and Attack Titan, were in Marley's possession.
Each Titan has their own set of skills, as well as their own disadvantages. For instance, the Colossal Titan is the largest; however, he is also one of the slowest. Meanwhile, the Cart Titan can maintain her form the longest and has remarkable endurance, but she isn't as tough as Shifters like the Armored Titan.
While they each have individual skill sets, some share similar traits, like the Female and War Hammer Titan, who both have advanced hardening skills. All Shifters can also regenerate limbs, even when their durability varies. Furthermore, they not only maintain their memories, but they can also access the memories of past Shifters. Plus, they maintain their intelligence, with several demonstrating the ability to speak in their Titan forms.
Shifters are also more proportional than Abnormal and Pure Titans, as seen with Armin. His Pure Titan form is emaciated and disproportionate, but his Colossal Titan -- regardless of size -- is more anatomically "correct." This, along with their intelligence, makes their Titans easier to maneuver, unlike Pure and Abnormal Titans, whose movements can be chaotic.
Despite the advantages of being a Shifter, there is a major downside. Unlike Abnormal and Pure Titans, Shifters have a lifespan of 13 years because of the Curse of Ymir. Furthermore, they must be eaten by another Titan in order to control who inherits their powers, otherwise, a random Eldian will become the next Shifter, making the Shifters' futures grim no matter what.
