Mage Meadowbrook is a pony figure of legend, and one of the Pillars of Equestria that once lived in Hayseed Swamp.
History
Long ago, she studied medicine under her mother and kept multiple journals. In one of her journal entries, Meadowbrook contends with a Swamp Fever epidemic that infects her mother and fellow villagers. While searching for a cure, she discovers that Flash Bees are immune to the disease-spreading flower's poison.
Using her healer's mask to shield herself from the bees, Meadowbrook collects some of their honey and uses it to develop a cure for the epidemic. Afterward, she dedicates her life to helping other sick ponies across Equestria. In the present, Meadowbrook is stated to have mysteriously vanished without a trace one day, and Cattail is her only known descendant. When Zecora comes down with Swamp Fever, Fluttershy cures her by using the notes and healer's mask that Meadowbrook left behind.
Season 7
She returns to present day after the Harmony Gems bring them back, and she joins the others in fighting the Pony of shadows to put him back into Limbo.
My Little Universe II
She briefly appears as part of the Pillars during the three-part finale, fighting Grogar's Army in the Realm of Corners.