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 slapped by her fishtail. Later, she is sent to stop Mario and his friends journey after Goro's defeat. After the heroes split up, Mario encounters Mad, disguised as a beautiful human woman. Using her mermaid magic, she manages to hypnotize Mario into carrying 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 tries to bite his head off. However, the Toad villager, followed by some of his friends, tosses him the Yūsha Kinopio Kamen, which he quickly wears, causing Mad's fang to shatter as she bites the iron mask. In pain, Mad releases Mario and the Toads toss rocks at her until she is overwhelmed by them, presumably perishing like her allies have in their own ambushes.

Super Mario-kun
Mad appears in Super Mario-kun only in chapter 11 of volume 12, where she is stated to be the water fairy of Peaceful Woods corrupted by Wario polluting the river. However, Mad is seen once in her mermaid form as her real form seems to be the water itself, forming an evil grin with some waves 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 urinates her out. Now free from Wario's evil toxin, Mad is reverted to her pure state: an anthropomorphic fish in a dress.