As far as i know all Pure Titans were made with a Titan's spinal fluid. I am wondering... if used spinal fluid was of for example Female Titan - wouldn't it make a female type pure titans? The same go for every other Titan. And for example Rod Reiss - IMO - He had used Colosal Titan spinal fluid as a titan serum. Wall Titans also might have been treated by it. I know there is a hole in this theory - Zeke's Titans had no fur.