Dreamy Mario greatly resembles Mario except that he has a shadow aura around him.
During the course of the battle, Dreamy Mario fights alongside Antasma (who has Princess Peach captured). Dreamy Mario mainly attacks by summoning a bunch of clones then jumps on Mario. Dreamy Mario will also sometimes change his position to try and trick Mario into attacking one of his clones instead. Dreamy Mario and his clones will also run to the background while Antasma fires either fireballs, coins, or mushrooms at Mario. Also if Mario hits one of the clones, they will jump into the air and attempt to land on him. During the second phase of the fight, Dreamy Mario organizes his clones to make it harder to tell which is which. Also during at one point, Dreamy Mario will run into the background and he and his clones will attempt to run into Mario. Antasma will even fire purple smoke to blind the player.
The key to winning this fight is to attack the real Dreamy Mario. When Dreamy Mario first summons his clones, the real one is always in the middle jumping. Mario can also heal during Antasma's fireball attack if a Mushroom shows up. Other than that, it's just simple to keep jumping on Dreamy Mario until he is defeated.