If a source you control would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.
9/29/2017 If a creature with trample you control would deal combat damage to a blocking creature while you control Angrath’s Marauders, you must assign its unmodified damage. For example, a 3/3 creature with trample blocked by a 2/2 creature can have at most 1 damage assigned to the defending player. It will then deal 4 damage to the blocking creature and 2 damage to the defending player.
9/29/2017 If an effect such as that of Chandra’s Pyrohelix asks you to divide damage among targets, you must divide the unmodified damage before doubling it.
9/29/2017 If you control a second Angrath’s Marauders, damage dealt by sources you control will be multiplied by 4. If you control a third, it will be multiplied by 8, and so on.