You should mention that the POW Block can pretty much nullify the effect of items, should you get hit by both at the same time.
Say if you got hit by a POW and a Red at the same time, the Red will do nothing, so long as you are still spinning from the POW Block.
This also works with, to my knowledge...
Normal Shells
Bananas
Lightning
Fake Item Boxes
...and that is all.