Madame Hydra is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Whenever you cast a Villain spell, create a 2/1 black Villain creature token with menace. (It can't be blocked except by two or more creatures.)

How it works : Madame Hydra

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Madame Hydra.

Madame Hydra, Reanimated

Menace (This creature can't be blocked except by two or more creatures.) Madame Hydra gets +1/+1 for each creature card in your graveyard. Whenever Madame Hydra enters or attacks, mill two cards. (Put the top two cards of your library into your graveyard.)