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Ōsama (Japanese: 王様, meaning "King") is the king of the dream world of Subcon. His sole appearance is in BS Super Mario USA, in which he is solely referred to by his kingly title in both dialogue and the closing credits, with no proper name ever being given.
Ōsama rules Subcon peacefully along with many of the fairies also known as Subcons, although he himself is human, as is his right-hand man. His world was attacked by the 8 bits, led by Wart, in both Super Mario Bros. 2 and its pseudo-sequel, BS Super Mario USA, although the king only appeared in the latter game.
BS Super Mario USA
After their defeat in the first game, Wart and his cronies escaped to another dream realm and laid low for some time, before returning to Subcon once again. This prompts Ōsama to call Mario, Luigi, Princess Peach and Toad back to Subcon using the power of the stars.
While Mario and the others battle Wart's army, images of the main characters, both heroic and villainous, appear on screen, delivering commentary and assisting the player on their quest. Like the other characters, Ōsama can either cause earthquakes like a POW Block, allow characters to make heavy stomps on the ground, transform Mario into his invincible form, destroy all enemies of the screen's range, or give bombs to him.