Maro's Gone Nuts

(12/11/2019)
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.

(12/11/2019)
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.

(12/11/2019)
Double strike isn’t an effect, so it’s not doubled.

(12/11/2019)
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.