The fourth and final season of Attack On Titan is currently airing and questions about the Nine Titans are finally being answered. All of the Shifter Titans have now been revealed and their human identities shown (except one, as of the time of writing).
One of the more obscure Titans in the Attack On Titan anime is the Cart Titan, which was first shown in Season 3's Episode 16, "Perfect Game." So far, not much detail has been revealed about the Titan itself and its holder, but here's what we do know so far about the Cart Titan.
As revealed in Season 3 of the anime, the Cart Titan is physically different from a standard Titan, Pure or Shifter. It has a quadrupedal form, allowing it to use all four limbs for movement. This gives it a major advantage on two fronts: one, it can carry things on its back, and two, it is extremely agile. In Season 4's Episode 1, "The Other Side of the Sea," we see the Cart Titan in its full militarized capacity, acting as a mobile machine gun in a war between Marley and the Mid-East Allies.
It's also a very versatile Titan. Even for a purely defensive or supportive strategy, the Cart Titan is extremely useful. It can carry a huge amount of supplies on its back and bear the burden more easily than upright Titans. Its ability to move on four limbs also gives it a severe advantage when it comes to sheer speed. It can move almost as fast as the Jaw Titan, which is pretty darn fast. It's an absolute asset for Marley and their military.
Additionally, the Cart Titan has a massive amount of endurance. It can withstand long journeys or battles without rest in Titan form, for months and months at a time. It is not easily tired out and can retain its Titan form for longer than the other Shifter Titans. These perks come with a drawback though -- the Cart Titan doesn't have the same regenerative speed as the other Titans. Therefore, a major blow will take it out of battle.
The holder of the Cart Titan is an Eldian Warrior of Marley named Pieck Finger. From what's been revealed so far about her character in the Attack on Titan anime, Pieck seems gentle and level-headed. She's often seen with a small smile on her face, giving her a very approachable demeanor. The contrast between her human and Titan form makes her an interesting choice to be the holder of the Cart Titan, arguably the strangest Titan of all.
A side effect of the Titan's quadrupedal form is that, after prolonged time spent in Titan form, the holder loses the ability to walk normally as a human for a while. Demonstrative of this is Pieck is walking around on all fours in her human form, claiming it feels "more natural." When she does stand, she's seen with a crutch. Though the effects of her Titan form are temporary, it's the only Titan that affects its holder after the transition back to human in this way.
With a limited number of episodes left of the final season, more about the Pieck Finger and her Cart Titan is sure to be revealed. Hopefully, before Attack On Titan comes to an end, we'll be able to fully understand the strangest of the Nine Shifter Titans.