By bombing Donation Machines, Isaac can earn more money than is taken from the machine, giving an endless supply of coins until the machine breaks or he runs out of bombs.
When used while fighting Greed, Hangers, or Keepers, every coin knocked out of Isaac will be worth two coins, allowing Isaac to net a profit.
Coins dropped when taking damage from enemies such as Greed, Hangers, or Keepers have a chance to be doubled, allowing Isaac to potentially recover all lost money or even net a profit.
Synergies
Contract From Below: Single pickup drops have a 2/3 chance to be doubled, which then become their doubled versions by Humbling Bundle.
This results in an average increase from 1.33x more pickups to 2.67x more.
This results in an average increase from 1.33x more pickups to 2x more.
IV Bag + Old Bandage + Humbleing Bundle / Maggy's Bow: The damage from IV Bag has a chance to spawn 2 hearts, which can be picked up to create further coins and possibly even heal hearts with enough Luck.
Humbleing Bundle only has a 50% chance to double the hearts dropped, but Old Bandage may still drop 1 heart.
The Jar: Allows for replicating hearts. Using the jar with 4 hearts inside it will cause 8 to drop, allowing Isaac to create an infinite amount of Red Hearts.
The item is a reference to Humble Bundle, collections of games and soundtracks that are sold online through a "pay what you want" system. The original The Binding of Isaac was represented in three humble bundles.
"Humbleing" is a common misspelling of the word "humbling", and may be a further pun on the reference to Humble Bundle.
All the files related to the object, such as graphics and animations, use the correct spelling in their names.
The description and writing on this items graphic is a reference to picking up double bombs in the original The Binding of Isaac where the message "1+1 Free!" would pop up in the bottom right whenever picking up a double bomb.
Transforms all 
Bombs, 
Keys, 
Pennies, and 
Red Hearts into their respective Double versions.
All 
Nickels or 
Soul Hearts, etc., are not doubled.
Donation Machines, Isaac can earn more money than is taken from the machine, giving an endless supply of coins until the machine breaks or he runs out of bombs.
Greed, 
Hangers, or 
Keepers, every coin knocked out of Isaac will be worth two coins, allowing Isaac to net a profit.
Contract From Below: Single pickup drops have a 2/3 chance to be doubled, which then become their doubled versions by Humbling Bundle.
IV Bag + 
Old Bandage + 
Humbleing Bundle / 
Maggy's Bow: The damage from IV Bag has a chance to spawn 2 hearts, which can be picked up to create further coins and possibly even heal hearts with enough Luck.
The Jar: Allows for replicating hearts. Using the jar with 4 hearts inside it will cause 8 to drop, allowing Isaac to create an infinite amount of Red Hearts.
BOGO Bombs: No further effect.
The Binding of Isaac: Rebirth
