From what I can gather from chapter 63, I have these thoughts.
1. Obviously, the power Frieda had was the 'Coordinate' which Grisha stole, and then gave to eren, but why did Grisha want it so badly? From how Grisha was acting (very nearly crying) he was begging for the coordinate and trying to convince the Reiss family his plan (what ever it was) could work, so he probably never intended to kill them all originally
2. I think the reason eren forgot everything till now was because, since Grisha ate Frieda and absorbed her coordinate power, he must of absorbed her ability to make people lose their memories, which makes sense since Grisha was physically holding eren the entire time, and the last thing he remembers is waking up in a barn after the fall of wall Maria in the refugee camp. Of course, this should mean that eren should have this ability as well, but that's where my theory starts to develop holes.
3. We know now how eren has flashbacks of Frieda from her point of view, because for all intents and purposes, Frieda is inside him
But I now still have 4 questions
1. How did Grisha even create the titan serum in the first place and how did Rod get it?
2. Can all the reiss family turn into titans? If so, does Historia's half bold relation mean she needs the serum?
3. If the reiss family have had this power in their bloodline, and knew about it, why was it not used to control titans
4. This is the most curious thing I noticed..... How, if the reiss family went into hiding, did bertholdt, Annie and Reiner know to target the coordinate.... This has to mean there is a relation between the reiss family and the 'humans' living outside the wall
