Zombie Berserker 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.

How it works : Zombie Berserker

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 Zombie Berserker.

Rise of the Dread Marn

Create X 2/2 black Zombie Berserker creature tokens, where X is the number of nontoken creatures that died this turn. Foretell {B} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Draugr's Helm

When this Equipment enters, you may pay {2}{B}. If you do, create a 2/2 black Zombie Berserker creature token, then attach this Equipment to it. Equipped creature gets +2/+2 and has menace. (It can't be blocked except by two or more creatures.) Equip {4}