Ok sooooooo lol Near the end of his route after his talk with Sydney at that point the hysteria has him right because Sydney is dead. well because of that he goes crazy and somehow manages to catch himself on fire. Literally his skin burn off. It freaks Carl and that salamander guy (forget his name) out. This seems to also be the way he turns into the very monster that was attacking them in his and Leos route. or the monster takes over his body and hes just conscious about it idk because obviously he wasn't the one attacking them when he was there being attacked with them. The part where he goes bling his eyeballs have melted out of his sockets at that point i believe and remember at some point during his route someone describes the monster face as an electrical socket? Flynn develops the same look at this point. Now right before the end remember he was in some weird place? a closet I think and a little girl opened it and spoke? now think back to Leos route where Jenna mentions to chase that she remembers seeing a monster like figure when she was younger but ignore it because she thought it was due to stress or something. that monster was/is Flynn. I think i explained it to the best of my memory you'll have to go back to get further detail but somehow Flynn becomes that creature and gets caught in a time loop that part if confusing itself but maybe its just because that general idea of echo is a loop. history repeats itself.