Mad

Mad is a boss that appears in the NES version of Wario's Woods. She is a green-haired, red-tailed mermaid with a crown and pearl necklace.

''Wario's Woods
Mad is the third boss that Toad faces, appearing in round 29. Like all bosses, Mad can create more enemies and teleport around the stage, and instantly KOs Toad if she reappears on top of him; she can also temporarily freeze Toad's sprite helper.

Super Mario (KC Deluxe)
Mad appears in two chapters of the Wario's Woods adaptation. She is summoned with Boom and Seizer by Fauster, after regaining some of his powers with Wario sacrificing Baby Luigi to him. Wario initially tries to hit on her, getting immediately slap by her fishtail. Later, she is sent to stop Mario and his friends journey after Goro's defeat. After the heroes' group split up, Mario encounters Mad, disguised as a beautiful human woman. Using her mermaid magic, she manages to hypnotize Mario into carry her outside the forest, leading him away from Fauster's lair. Wanda, who attempted to stop Mario, creates a potion with the intent of waking him up, but (as always) her potion explodes. Hearing the explosion, however, frees Mario from the hypnotic mermaid voice, so Mad regains her true form and coils Mario with her tail and goes to bite his head off. Luckily for Mario, the Toad villager, followed by some of his friends, tosses him the Brave Toad Mask which he quickly wears and Mad's fang shatters as she bites the iron mask. In pain, Mad releases Mario and the Toads toss her rocks until she is overwhelmed by them, presumably perishing like her allies have in their own ambushes.

Super Mario-kun
Mad appears in chapter 11 of volume 12, where she is stated to be the water fairy of Peaceful Woods corrupted by Wario polluting the river. Mad is however seen once in her mermaid form as her real form seems to be the water itself, forming an evil grin with some wave resembling her bangs and crown, capable to also change between liquid, solid and gaseous state at will. None of Mario, Luigi, Toad, Birdo and Yoshi's attacks do anything to her, until Yoshi drinks her up and pees her out. Now free from Wario's evil toxin, Mad is reverted to her pure state: an anthropomorphic fish in a dress.