At the end of the anime Attack on Titan: The Final Season Part 2, Eren has transformed into a completely new Titan form. He becomes significantly larger, resembling a colossal structure rather than a human-shaped Titan. This Titan form appears after he has a direct encounter with his brother, Zeke Yeager, awakening the true power of the Founding Titan.

Furthermore, Eren’s inheritance of the Attack Titan and the War Hammer Titan also plays a crucial role in shaping his Final Titan form, which is the largest Titan ever seen in Attack on Titan. This creature surpasses not only the Colossal Titan but also the Titan form of Rod Reiss.
Before the emergence of the Final Titan, the Rod Reiss Titan was considered the largest, standing at an impressive height of 120 meters when in its “sitting” position, dwarfing both the walls and the Colossal Titan of Bertolt Hoover. Due to its massive size, the Rod Reiss Titan always exuded a tremendous amount of steam, lacking any substantial flames near it and continuously radiating heat.
Below is a CGI model of the Final Titan, introduced by AOTWiki on Twitter:

Looking at the image above, one can see that Eren’s final Titan form is truly massive, seemingly enveloping the entire Shiganshina district. Viewers also notice that this Titan form has legs. However, due to the immense weight of its massive structure, the mobility of the body feels restricted, making it appear as if it is lumbering rather than moving gracefully.
Below are some netizen comments:
– How can Eren possibly move in this gigantic form!
– It’s surprising to realize he still has legs.
– These legs look so “baby” compared to that colossal body.
– The legs of Final Titan Eren are even taller than the Rod Reiss Titan.
– I keep thinking Final Titan Eren resembles a giant slug.