Trying to answer some questions! In the remake you only need 20 gems to unlock IF mode, as there’s only 20 i believe, when looking online i saw an attic being mentioned, i did 3 run of normal mode and 2 bloody ones, never seen it Yes you can obtain the 20 gems by skipping prologue and also in bloody mode since its faster If anyone has any questions feel free to ask
You have to go into the archive room. Best if you do somethin in there, but when you come out a mission should pop up about a Noise in West Hallway. Hide behind the statue, and go for the gem once in the clear. Hope that helps~