This isn't uber-creative or anything, but there were two missed Discern Realities moves in the game I ran a few weeks ago.
The first one was when a character listened at a door (which, upon retrospect, didn't require him to make the move at all). I told him that he heard gently lapping water, as if there was a large body of water on the other side. Which there was; the "room" on the other side was a 30' diameter underground lake with an Otyugh lurking in it.
There really wasn't anything else going on in the location the characters were in, I had already used previous misses to set up stuff in other locations (thinking offscreen), and I couldn't think of a move that fit the consequences of the action (which is why I probably shouldn't have required the move at all). So I just "banked" my GM move for use later. I then used it to deal damage with the Otyugh when the characters turned their back on the open door. Or rather I tried to. There was a mix up in player/GM communication and it turns out the characters had closed the door before they turned. I turned it into a Defy Danger move to get the door shut before some tentacles came through.
The second one was when someone went to explore a dead end hallway. It was getting towards the end of the session, and so I decided to go nasty; I put a Green Slime on the ceiling to put them in a spot. I guess the move wasn't that hard, as I gave the character a Defy Danger move to get out of the way before it dropped on him. I suppose I could've just dealt damage as it reached out and engulfed him with it's pseudopods, but that seemed unfair.