A kid who comes to the conclusion that he switches between dimensions every day because his family keeps on telling him that something different happened than what he remembered, but then eventually decides that he's insane, which he isn't
A guy who can lucid dream and sleepwalk, and can influence the world around him as if it were a dream, but if he is woken up, everything he did changes back, and if he wakes up on his own, it stays
A world subject to an onslaught of monsters that are attracted primarily by light
During the day, they all fly up toward the sun, but at night, they fall upon the earth and ravage wherever has the lights on last
Probably not great ideas, but that's all I could think of atm
They're probably a bit too dark (pun somewhat intended) excepting second one, which you could do a lot with
