Aunt Dahlia

Aunt Dahlia is the main antagonist in the short story "An Old Story" from Still More Tales to Give You Goosebumps, and its television adaptation.

"An Old Story"
Aunt Dahlia is a witch who goes around claiming to be related to various families as a "great aunt," and then ages their children into senior citizens with enchanted prune cookies to marry them off to her friends, including Lillian and Mimi, for a price. When Tom threw a pitcher of prune juice at her, her face melted away to reveal a skull, then her whole body collapsed into dust.

Goosebumps: The Game
She also appeared as an enemy in Goosebumps: The Game. She's defeated the same way as the book with prune juice. Once she's defeated, the player must take the cassette tape she leaves behind.

Horrors of the Witch House
Aunt Dahlia is referenced in the Goosebumps story arc Horrors of the Witch House, when Clarissa tags her on what appears to be the social media equivalent of Twitter for witches.

Trivia

 * Aunt Dahlia is one the very few Tales to Give You Goosebumps monsters to appear in a video game.