Having a dream-based character who literally only exists on a dream plane (and can therefore only interact with people when they are dreaming, or more rarely, when they are delerious or drugged) could be interesting.
Or a material person with a 'dream travel' sort of teleportation. Various other teleporters might be limited to only step into and out of shadows, or water, or mirrors, or power lines, but this one can only step into the dreams of a sleeping person near them, and out again from a sleeping person's mind perhaps many miles away. (Which requires some stealth and shenanigans, since you'd often be appearing in people's bedrooms, and maybe have to coast around for an 'exit point' from the Dreamlands that's 'some dude who nodded off on the bus' or 'some lady catching a nap in the break room'... Cause, otherwise, awkward!)