Here is a list of a few (Fake) Mockingjay Spoilers.
Katniss is really President Snow's daughter and it was all an act.
Gale commits suicide because Katniss chooses Peeta.
District 13 is really Knome City.
Peeta isn't really taken hostage, they just tell Katniss that to scare her into going to District 13.
Prim and Katniss's mother are on the ship they're just hiding and waiting to jump out and yell "Surprise!"
President Snow commits suicide!
Haymitch is really Robert Downy JR in disguise.
Gale becomes Peeta's best friend.
Anything else I should add?