Oh, just discovered an unusual combo of blocks. I have no idea how this might be useful, since I can't see a way to communicate this to players, but Burners are NOT blocks. When you place a Burner, it will place on top of the block beneath it, but NOT overwrite it.
Now what can you do with this? Well, the burner block will inherit the properties of the block it's on. So, if you place it on a Spike Trap, it will be harmful to touch, which is a jerk move since that is not a common use of them. But perhaps more interestingly, you can place it on top of a ?-Block and hide items in a Burner. Anything that goes in a ?-Block will work since it IS a ?-Block. Mushrooms, Fire Flowers, Vines, Giant Flying Bowsers, you name it. And if you use a Note Block, you should be able to trigger it from above, too. And basically trip Mario if he's running across it.
I am not entirely sure how this will be useful, but it's a weird thing I thought I'd share. Use it for good (or trolling) as you see fit.