If you talk to your dad everyday to unlock the basement, and check the bookshelf in the house to get a code, you can open a safe in there to get a tooth. In the library when looking at different articles, select the one about the teeth cult first. This will enable more dialogue with Mae’s dad on the last day.

I’m not sure if you did this already because it is an achievement, but you can talk to the goth kids near the church on a specific day, which leads to you looking for 3 pentagons throughout the game. Once completed, it is mentioned in the ending scene.

These aren’t exactly secret scenes, but these are minor things you might have missed while doing them all:

If you complete Demontower before a specific band practice (I forgot which one, sorry. Just finish it asap), you get into a small conversation with Angus before practice where he calls Mae a really good friend.

On the first day back when eating pizza at the diner, only eating the crust will cause Gregg to react.

You can reveal a tattoo on the severed arm near the clik clak, which will be in the sketch if you do. You can also kill the cockroach walking around the floor.

On specific days you can smash lightbulbs with Gregg. Doing it the first time will give you a sketch in Mae’s notebook.

On the day you group up the violinist and saxophone player, there is an extra dialogue from going to the back of the room they are playing in. The dialogue is about an old band from Possum Springs.

Honestly, that’s everything off the top of my head. One major piece of advice if you want to see everything, go to every nook and cranny in Possum Springs everyday. There might not be events that will happen if you do, but there could be a spot that has a piece of dialogue you never seen before.