Box of Paper Slips

Paper Slips are magical pieces of paper in the world of BFDI that turn into dollar bills when a number is written on them. The commercial debuts in Crybaby! and has been used several times by Pen and Leafy.

Pen

 * Vomitaco: Pen asks how much he has to pay for Leafy to lend him a taco, and the answer is such an expensive price. Pen says "Well, what do you know?" while holding up a dollar bill with the price in one hand and the box of paper slips in the other. Unfortunately, this makes the eliminated contestants know he cheated, making him fall into the danger zone and, ultimately, eliminating him.
 * Gardening Hero: His re-campaign speech is if someone votes for him, the voter will get 5,000,000,000,000,000,000,000,000,000,000 dollars while holding the paper slip containing so. Next episode, after he learns he didn't get enough votes, he recite the usernames of the people who voted him and says "I owe you 5,000,000,000,000,000,000,000.... dollars each because I can't afford to pay you right now" before getting teleported to the TLC again.

Leafy

 * Return of the Hang Glider After Firey rejects Leafy from Dream Island, Leafy calls up the announcer and gives him $10,000,000,000 drawn on a paper slip to buy Dream Island to get revenge on Firey, which leads to the plot hole of this episode. In the end, when she almost dies, Firey saves her with a hang glider and reveals his true feelings for her.

Commercial
Advertiser (Yellow Face): You need some money FAST and SOON? Then buy our box of paper slips! At first it might just seem like a blank slip of paper, but you just scribble a number on it, and POOF! It's a dollar bill! This person bought a TV. [$2,000] This person bought a house! [$500,000] THIS PERSON BOUGHT THE WORLD!! [$10,000,000,000] So yeah, BUY NOW!

Trivia

 * It is possible that Book might have used the paper slips in No More Snow! because she had went on to make billions of dollars.
 * Paper slips may have overtook the green dollars from Sweet Tooth as official currency, but that is unsure yet,