Bubble Gum 
and HE Bubble Gum 
are items that increase the chances of obtaining items.
You can obtain Bubble Gum from Lucky Me and from the Collector Keeper. You can make HE Bubble Gum from the Guardian Keeper.
There are two types of Bubble Gum: regular Bubble Gum [Item ID: 12210] which says that it increases drop rates to 200% (2x the standard rate) and HE Bubble Gum [Item ID: 12412] which says it increases drop rates to 300% (3x the standard rate). Neither of the descriptions are to be taken literally. They do not increase the actual drop rates.
When using Bubble Gum (regular), killing a monster will behave as though you killed it 2x, giving you two chances of obtaining the item. Say you're hunting 
Lost Soul (drop rate: 10%) with HE Bubble Gum. This is the process:
- Using Bubble Gum, you killed Soul Taker for 10% of obtaining Bubble Gum. Did the player receive it? If so, end roll 1. If not, Step 2.
- Using Bubble Gum, you killed Soul Taker for 10% of obtaining Bubble Gum. Did the player receive it? If so, end roll 2. If not, Step 3.
- Using Bubble Gum, you killed Soul Taker for 10% of obtaining Bubble Gum. Did the player receive it? If so, end roll 3.
As you can see, the drop rate is still 10%, but it's as if the gum gave you more chances of obtaining the item.
Stacking and Function
Q) Does using more than one Bubble Gum stack? Do Bubble Gum and HE Bubble Gum stack? Does Bubble Gum stack with the Bubble Gum effect from the Collector/Guardian set?
No.
Bubble Gum/HE Bubble Gum do not work on:
- Wandering Spirit 'special' prizes (30000 Gold Box, Blossom Wings, Hat of Possession)
- Laboratory Keycard
- The Key of Integrity, Courage, Wisdom, Humility
- Seal of Excavation
- Lucky Me