The castle at the middle of the Oniverse is under attack. The dream denizens of the oniverse rush to construct their castle defense against three monster attacks. Towers let you see what is coming. Keeps will help minimize damage. Ranks can reduce the effects of the traitors found within your walls. Of course, the denizens have special powers of their own to help in the defense. Will you be able to survive all these attacks?

Castellion is a tile-laying game in which you create parts of the castle for defense against monsters. Every turn you flip over a tile and either use its special ability or place it as part of your castle. The more towers and keeps you form, the better your defense against attacks. Ranks keep traitorous tiles from affecting you fully. When all three monsters have attacked and you still have a base of six tiles, you win the game.