Attack On Titan season 4 ended episode 12 with a shocking revelation - there's a spy in the midst of Paradis Island - one that could signal some really bad things that are about to go down. (Spoilers) The final scene of "Guides" shows how the residents of Paradis Island are reacting to the rise of Eren Jaeger's militant splinter group, the "Jaegerists." As people debate the drastic sudden turn in Eldian politics, the camera pans over to reveal one "townsperson" quietly observing the turmoil, while pretending to read a paper. A close-up shot reveals that the person in question is none other than Pieck!
Pieck Finger is the quiet sullen girl in the Marley Warriors unit - who also happens to be the inheritor of the Cart Titan. Pieck's Cart Titan proved to be one of the most unexpectedly formidable special Titans in the punch. We got a taste of what the Cart Titan can do during the "Return to Shganshina" arc, but the anime's recent "Marley" arc showed just how dangerous the Cart Titan is in its full armored battle gear, with the machine gun pillboxes strapped to its back. In fact, when Eren Jaeger launched his ambush against Marley, it was Pieck's arrival with the Cart Titan that nearly turned the tide of the battle, as the Cart was able to snipe the Survey Scouts on their ODM gear.
The Scouts nearly took out Pieck's Cart Titan thanks to Sasha's sniping and Jean's Thunder Spear, but Pieck has proven to be as quick and cunning as any of Marley (or Paradis Island's) best warriors. Not only did she manage to survive Paradis Island's ambush - it was Pieck who pieced together that it was Yelena who betrayed her and Galliard during Eren's ambush, as part of a larger plan by Zeke Jaeger.
Last we saw, Marley's General Theo Magath presented Pieck's deductions to Marley's Warrior Unit, sparking renewed fire in Reiner Braun and the rest of the unit, to get revenge on Paradis Island. Reiner stressed that they needed to counterattack soon, before Zeke can strategize against their full war effort - and based on the fact that Pieck has infiltrated Paradis Island, it looks like that's exactly what's going down.
Pieck Finger has become a fan-favorite for being a quiet, cunning, badass in Marley's Warrior Unit - arguably the best candidate to go toe-to-toe with Mikasa when Marley and Paradis ultimately collide again. If Pieck is in Paradis, it's a really bad sign: you can bet the Cart Titan never travels alone, or without supplies. With Pieck's level of intelligence, it's also now a big question of whether or not Paradis Island's Premier, Zachary, was killed by Jaegerists, or was a target of Pieck and her comrades, as means to de-stabilize Paradis' military and populace. Because if they did... it's working.