How do you think Bowser will work as a playable character and a stage hazard at the same time?

In the trailer we see him being played as in a few minigames, but then we also see him on his own board as the villain (he's also on Mario's Rainbow Castle). Would he only be playable in certain modes, because we don't see him played as in any board footage. My best guess would be either he's exclusive to the Free Play mode, or you can unlock him after beating his board. What do you guys think?