One day you realize that you keep seeing Carl in your dreams. Every night. He's not really in them, though. Usually he's just sitting somewhere, watching. Once he was reading a book.
You come home to find all the food in your pantry replaced with doll parts. Everywhere you look, there are naked plastic arms, or legs, hands, feet, torsos. Stuffed into a flour sack, bundled like dried fish, immersed in jam jars. Where your garlic braid once was hangs a braid of doll heads, neatly hung on its hook.
Change an NPC's personality radically, overnight! When someone notices, make them read the situation and tell them something scary.
Sometimes, people go missing, and a few days later they come back, but they don't remember that they've been gone.
When it rains, everyone bursts into tears.