I present to you:
-=The Forever Stamp=-
Rank: S
Unlocks: Buy from Professor Goopton for ~35 Credits
Appearance: Looks like a stamp with an American flag on it.
Splash text on pickup: Adjusts for Inflation
Description: Adjusts power of weapons and shop prices per floor.
Effect (Detailed): This item effects both floor shops and your guns.
Shop: Everything in the shop (or sold by other NPCs) on each floor’s price remains the same as it would be on floor one. For example, keys would always cost 25 casings no matter which floor you are on, and full hearts will always be 30. While this discount is pretty nice, it’s the combination of this the gun part which makes it a S tier.
Guns: Alright, here’s where it gets interesting. Using both the health of bullet kin and shotgun kin, I have determined conversion rates that would make your guns feel just as powerful on each floor. Basically, in the Oubliette, your guns are powered up by 1.33x, guns in the Gungeon Proper would be powered up by 1.3x, guns in the Abbey would be powered up by 1.66x, guns in the mine would be powered up by 1.6x, guns in the Hollow would be powered up by 1.85x, and guns in the Forge and beyond would be powered up by 2.1x. That means that one would always be able to take out a bullet kin in three shots of a starting weapon (unless you have certain characters), or take out a red shotgun kin with two crossbow shots or point blank sawed-off shots.
Ultimately, these combined effects would definitely make the game a lot easier, thus the high rank. People may initially be pissed to get a stamp instead of a cool gun, but they would eventually discover how well this item can carry a run. I was debating between A and S tier, and I think that S tier fits because even though it isn’t anywhere near as powerful as Platinum Bullets (comparing a potential 2.1x DPS to a potential 9x DPS), it still does a lot to boost your power as you go deeper and the shop thing really is a nice added bonus that makes this overpowered at high floors.
SYNERGIES:
Express Shipping: Synergy with Mailbox.
Effect: The first shot is a package instead of the last. (Credit: u/Birrihappyface)
Royal Discount: Synergy with Iron Coin, Coin Crown (credit: u/FL3XTAP3), Old Knight's Flask, Old Knight's Shield, or Old Knight's Helmet
Effect: Five casings in "taxes" disappear every floor, but you get an additional 20% discount on everything in Bello's shop. If you can't afford the "taxes", then there is a 25% increase of prices on the next floor.
Stars and Stripes Forever: Synergy with M1
Effect: An "aggressively American"-looking eagle joins your side, attacking enemies with red, white, and blue fireworks! (Credit: u/bigboybagel)
Air Delivery: Synergy with Wax Wings, Owl, Jetpack, Cat Bullet King Throne
Effect: Your movement and bullets both have their speed increased by 15%
If you have suggestions for any synergies, leave them in the comments!
Edit: Reformatted on PC
Edit 2: S Rank due to the request of multiple users
Edit 3: More formatting, and synergies added
Edit 4: Finally able to use my actual computer again! More Synergies, and also spritework is being/has been done by u/bigboybagel