From Brotato Wiki
Item
Goldfish is an in-game item that can be bought from a Shop or can be found in a Crate. Most Items modify the Stats of the player, and some of them provide additional effects.
Notes
The Goldfish is a single use item that is used during Shopping, similarly to 
Mirror.
When you reroll the shop while having a goldfish active, the items and weapons on the new reroll will be +1 tier higher than they would've otherwise have been. So if the shop had selected to give you a tier 2 weapon, that becomes tier 3, and it then chooses the specific weapon to give from among tier 3 weapons.
After being used, the Goldfish turns into a 
Resting Goldfish, which does nothing.
The tooltip can be a bit hard to understand. But the goldfish doesn't affect Locked items. And if you reroll while having locked items, you'll see less than 4 items/weapons that have their tier boosted by the goldfish, wasting some of the potential.
- Goldfish can make Tier 4 items and weapons show up in the shop before it would otherwise be possible. Normally Tier 4 can't show up before wave 8+.
- Cursed Goldfish upgrades the next reroll by 2-3 tiers. At +3, this guarantees a full shop of Tier 4 items.
- If you have multiple Goldfish active, for example after using a Mirror to buy two goldfishes, then only one Goldfish is used per reroll. It still only gives +1 to tiers.
- When playing
Curious be warned that since the Goldfish turns into another item after being used, it will show the Green icon. But you'll end up with 2 Used Goldfishes, which will give you -10% Damage.
Update History
- 1.1.0.0: Added to the game.