Not gonna lie, this looks like a good twist from the Destiny Board concept.

Disclaimer: I will not focus on Art or grammar, unless the latter would make the deck too difficult to understand. 

Next up, Kenji Aoi - and shout-out to Bakura's deck in Battle City Tournament.

So, first things first, it's a good encounter to throw at players as a one-off? Someone possessed by hostile force, like a Demon, is a staple for a reason, and can make for excellent drama. Even if this encounter references concepts from a campaign world unique to the creator, it's still easy to slot into other campaigns by just brushing aside those mentions. The Demonic Board was also a great Plan to Win by Bakura, and I'm glad to see it here in this format too.

Now, I do need to voice some misgivings about the other Plan to Win: Demonic Child. It has a dual problem, where the first one is that it doesn't really interact with the Gimmick all that much? Forcing someone to discard with every {Careful}-induced bounce is evil in the more fun way, yeah, but doesn't feel quite at home here? I honestly wish it would instead do something with the letters, since those do seem to be the theme carried along by the deck, and this would help the cohesion of it all. Maybe bring out a letter with each bounce instead?

Further, the instant win button there is a bit problematic, if it's played second (and I assume it's intended to be the second Plan to Win by nature of Demonic Board needing time). In a longer game, a Player Character will probably have emptied their deck entirely naturally when this thing comes to the Field, and that's just an instant Win without the conceptual countdown instant win cards should have. See above for the idea of it bringing out a letter with each bounce instead, or some such?

Still, good job!