Maro's Gone Nuts

• WWizards of the Coast2019-11-12
  Official Ruling
  Double strike isn’t an effect, so it’s not doubled.
• WWizards of the Coast2019-11-12
  Official Ruling
  An effect “doubles” if it instructs a player to double something, or if it replaces an event with “double that much,” “twice as many,” or similar.
• WWizards of the Coast2019-11-12
  Official Ruling
  An effect that increases something by a specific amount (such as the first ability of Jaya, Venerated Firemage) isn’t doubling, even if the result is double the normal result.
• WWizards of the Coast2019-11-12
  Official Ruling
  If two Maro’s Gone Nuts are on the battlefield, effects that double instead octuple. If three are on the battlefield, effects that double instead sexdecuple, and so on.

Rulings via Scryfall