The red monster is Flynn. Specifically Flynn from his route. The idea is that basically at the end of Flynn's route he became one with the Tide, which is basically the pattern in how the hysteria works. Tide rolls in when some kind of murder happens, rolls out when the hysteria is over. Notice how Flynn at the end of his route is showing up at specifically negative moments in character's past. He was in Jennas closet when hiding from her abusive father etc. Basically, the monster shows up when any sort of negative action occurs. Its a problem specific to the town for some presently unexplained reason, but there are theories. The monster isnt bending space time, space time is bending him. Every time the tide rolls out a piece of him is taken, not just mentally. Thats why the monster looks like beef jerky, he's being taken apart peice by peice until he is nothing, one with the tide. The monster in all routes is flynn from his route as the tide covers all routes simultaneously. To summarize, Flynn turns into the monster and then is dragged into other routes throughout different periods of time.