Mab, also known as Medb or Meive, is the queen of Connacht. Famous for her capricious nature and her many lovers, she wages many wars for sake of her continuance glory. The Cattle Raid of Cooley makes her cross path with her archenemy Cu Chulainn, who shamed her numerous times by slaying her pets, warriors, and handmaidens.
Queen Mab is immortalized in "Romeo And Juliet" in Mercutio's legendary monologue (Act I, Scene 4), which is often called the "Queen Mab Speech", which includes:
And in this state she gallops night by night Through lovers' brains, and then they dream of love O'er courtiers' knees, that dream on court'sies straight O'er lawyers' fingers, who straight dream on fees O'er ladies' lips, who straight on kisses dream Which oft the angry Mab with blisters plagues...
Queen Mab can be obtained through evolving High Pixie. Even though Queen Mab can be created via secondary evolution from Pixie, unlike Kurama or Wu Kong, she can be encountered in normal battle and can be persuaded to join the player's team.
"A queen appearing in Celtic mythology. She is the queen of Connacht in Ireland. Her name means "she who intoxicates." She is considered a goddess of the harvest and of rulership, owing to her many marriages with Irish kings. Queen Mab tried to seduce the Irish hero Cu Chulainn using her own daughter, but failed. In the end, enraged by the enormous losses he inflicted on the army of Connacht, she manipulated him into breaking his geis (taboo), weakening him, and then had him killed by her magicians. Mab's death is recorded in 11th-century documents. She is held to have been killed by a piece of hard cheese flung from a sling. Mab is also known as queen of the fairies, and is identified with the fairy queen Titania."
—Shin Megami Tensei IMAGINE Compendium
Queen Mab can only be acquired through fusion. She appears as a boss in the neutral path of the Foreign Country in the Woods quest.