Oh man, you guys are really on to something with that cloud theory. I'm not supposed to reveal inside information, but I just can't help myself, so I'll let you all in on the true secret behind the screen shot.
First off, there is no Bowser or Ridley in those clouds. Your seeing them is simply the result of the rather impressive ability of various parts of your temporal lobe, such as the fusiform face area and parahippocampal place area, to find familiar shapes and patterns in random and ambiguous visual stimuli.
However, there IS a secret in that picture. Look at the top left of the screenshot:
See that cloud on the top left? Look carefully. What does it look like?
If you said "Hmm, that cloud looks suspiciously like a condensed mass of red water droplets that have formed around some sort of condensation nucleus," then guess what - you're right on the money!
What this means, in case you haven't figured it out already, is that Nintendo's next playable character to be revealed is none other than a red cumulonimbus cloud.
I don't know it's official name or it's full move set as of this time; however, I do know about one move:
Move: Rainfall
Execution: Down and B
Description: Causes the cloud to go through the collision and wake capture process, which allows rising and falling water droplets to increase in weight and mass by forming together as one. These newer, badder-ass water droplets have the ability to overcome air currents in the cloud and the updraft beneath them, which allows them to fall on their unsuspecting victims, dealing 10-15% damage and slowing their movement speed by 5-10% for a short time (this slowing effect is due to the fact that their clothes/fur absorb the water, which increases their weight. This means that characters without clothing or fur are immune).
Hopefully Sakurai won't be too angry with me for revealing this; he's (she's?) just such an awesome character that I couldn't keep him (her?) a secret...