If equipped creature would deal combat damage, it deals double that damage instead.
If another creature would deal combat damage to equipped creature, it deals double that damage to equipped creature instead.
If a creature is equipped with a second Inquisitor’s Flail, combat damage dealt by and dealt to that creature will be multiplied by four. A third Inquisitor’s Flail would multiply the combat damage by eight, and so on.
If you divide the combat damage dealt by the equipped creature, perhaps because the creature has trample or is dealing combat damage to multiple creatures, you’ll divide the original amount and then double the results. For example, if a 5/5 creature with trample is blocked by a 2/2 creature, you can assign 2 damage to the blocker and 3 damage to the defending player. These amounts are then doubled to 4 and 6 damage, respectively. You can’t double the damage to 10 first and then assign 2 to the creature and 8 to the player.