Who is the 9th Titan shifter?
In Attack on Titan, Chapter 95, pages 16-17 we find out that the 9th Titan-Shifter is the


  War Hammer Titan, which is currently in possession of the Tybur family who currently resides in Marley. We also find out that the War Hammer titan is not used for warfare and has never been used against any enemy state (of Marley). It is important to note that the Tybur family was the first family of titan-shifters to rebel against King Fritz in the Great Titan War and they carry a lot of political clout. 


In Chapter 101, the identity of the 9th Titan-Shifter was revealed to be 


  Willy Tybur's sister.