From Brotato Wiki
Shop
The shop will offer 4 random items. These items will depend on your character, 
Luck, number of waves progressed and if you have chosen to lock it. Each item has a cost depending on its rarity and their base value. You can purchase unique items once.
Mechanics
Rolling
Rolling is done buy refreshing your shop for a certain amount of currency. This amount gets increased as you roll. 
Dangerous Bunny will allow you to have +1 roll for free each round (this effect stacks). Otherwise, you will have +1 roll for free when all 4 items in the shop has been bought.
| Number of rolling/Waves | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | N/A | 2 | 3 | 4 | 6 | 7 | 9 | 10 | 12 | 13 | 15 | 16 | 18 | 19 | 21 | 22 | 24 | 25 | 27 | 28 |
| 2 | 3 | 4 | 5 | 8 | 9 | 12 | 13 | 16 | 17 | 20 | 21 | 24 | 25 | 28 | 29 | 32 | 33 | 36 | 37 | |
| 3 | 4 | 5 | 6 | 10 | 11 | 15 | 16 | 20 | 21 | 25 | 26 | 30 | 31 | 35 | 36 | 40 | 41 | 45 | 46 | |
| N+1 | N+1 | 3(1+33%*N) | 4(1+33%*N) | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | ... | 28(1+33%N) |
Locking
You can lock as many items as you can which ensures your next shop will keep those items of your choice. This is very useful when you can't currently afford an item, or if you want to wait with buying an item. It is free to lock and unlock items and you can do it as much as you want.
When you lock an item, it does change or go away when you reroll the shop and it stays there until the next shop if you go to the next wave. Locked items' price doesn't change or inflate if you keep it between shops.
Combining
You can combine weapons by having two of the same weapon equipped. This will combine them freeing up a weapon slot and upgrading the item to a higher rarity.
Also, if you have filled your weapon slots and buy an exact rarity of an item you wield that is not legendary the item will automatically combine making it a higher tier.
Recycling
You can recycle your Weapons and Items found in Crates to get a percentage of their value back, at the cost of losing the item or weapon.
The default is to get 25% back when recycling. 
Recycling Machine can increase this value by 35% for a total of 60% back.
This stacks with the +25% from 
Entrepreneur for a total of 85%. Rewards for recycling are based upon the current price of the item, so it increases with inflation, but decreases if you have coupons, since it scales with your shop price secondary stat.
Elite and Swarm Radar
On danger 2+ the shop will display which waves contain which waves have swarms or elites in.
Inflation and shop prices.
Each item or weapon has a base price. When you see the item/weapon in the shop it will have inflation applied to its price. Even the first shop has already have inflation applied.
The equation is: Inflated price = Base price + (10% of Base price + 1) • Shop number.
So if an item has a base price of 90 and you see it in the first shop, it will cost 90 + (9 + 1) • 1 = 100 gold. And its price will increase by 10 gold for each wave/shop that passes.
Since the Equation includes a flat +1 in addition to the 10%, cheaper items will be hit harder by inflation, and will be slightly less cost effective late game.
Locked items are not affected by inflation if you keep them locked between shops.
Rarity of Shop Items and Luck
| Min Wave | Base Chance | +Chance per Wave | Max Chance | |
|---|---|---|---|---|
| Tier 1 | 1 | 100% | 0% | 100% |
| Tier 2 | 1 | 0% | 6% | 60% |
| Tier 3 | 3 | 0% | 2% | 25% |
| Tier 4 | 7 | 0% | 0.23% | 8% |
Calculation for chances are done by:
= ((Chance per Wave * (Current Wave - Min Wave)) + Base Chance) * (100%+Luck)
Chance per wave starts adding chance after the Min Wave.
This value cannot exceed Max Chance.
Rarities with 0 Luck
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tier 1 | 100% | 94% | 88% | 80% | 72% | 64% | 56% | 47.77% | 39.54% | 31.31% | 23.08% | 20.85% | 18.62% | 16.39% | 14.16% | 12.93% | 12.7% | 12.47% | 12.24% |
| Tier 2 | 0% | 6% | 12% | 18% | 24% | 30% | 36% | 42% | 48% | 52% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% |
| Tier 3 | 0% | 0% | 0% | 2% | 4% | 6% | 8% | 10% | 12% | 14% | 16% | 18% | 20% | 22% | 24% | 25% | 25% | 25% | 25% |
| Tier 4 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0.23% | 0.46% | 0.69% | 0.92% | 1.15% | 1.38% | 1.61% | 1.84% | 2.07% | 2.3% | 2.53% | 2.76% |
Luck increases these chances by x%, but that still cannot exceed the Max Chance.
For example:
- In wave 10 with 0 Luck, the chance for Tier 3 is 2*7 = 14% -- extrapolated: ( 2% * ( 10 - 3 ) + 0% ) * ( 100% + 0% )
- In wave 10 with 50 Luck, it increases by 50%, 2*10.5 = 21% -- extrapolated: ( 2% * ( 10 - 3 ) + 0% ) * ( 100% + 50% )
- In wave 10 with 100 Luck, it increases by 100%, 2*14 = 28% -- extrapolated: ( 2% * ( 10 - 3 ) + 0% ) * ( 100% + 100% )
- However, Max Chance for Tier 3 is 25%, so the chance for Tier 3 ends up as 25%.
Rarities with 50 Luck
Increases chances by 50% (*1.5), up to the Max Chance.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tier 1 | 100% | 91% | 82% | 70% | 58% | 46% | 34% | 24.66% | 21.31% | 17.96% | 14.62% | 13.28% | 12.93% | 12.59% | 12.24% | 11.89% | 11.55% | 11.21% | 10.86% |
| Tier 2 | 0% | 9% | 18% | 27% | 36% | 45% | 54% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% |
| Tier 3 | 0% | 0% | 0% | 3% | 6% | 9% | 12% | 15% | 18% | 21% | 24% | 25% | 25% | 25% | 25% | 25% | 25% | 25% | 25% |
| Tier 4 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0.35% | 0.69% | 1.04% | 1.38% | 1.73% | 2.07% | 2.42% | 2.76% | 3.11% | 3.45% | 3.8% | 4.14% |
Rarities with 100 Luck
Increases chances by 100% (*2), up to the Max Chance.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tier 1 | 100% | 88% | 76% | 60% | 44% | 28% | 24% | 19.54% | 15.08% | 13.62% | 13.16% | 12.7% | 12.24% | 11.78% | 11.32% | 10.86% | 10.4% | 9.94% | 9.48% |
| Tier 2 | 0% | 12% | 24% | 36% | 48% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% | 60% |
| Tier 3 | 0% | 0% | 0% | 4% | 8% | 12% | 16% | 20% | 24% | 25% | 25% | 25% | 25% | 25% | 25% | 25% | 25% | 25% | 25% |
| Tier 4 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0.46% | 0.92% | 1.38% | 1.84% | 2.3% | 2.76% | 3.22% | 3.68% | 4.14% | 4.6% | 5.06% | 5.52% |
Item & Weapon Chances
Item/Weapon Chance
Most waves have a fixed chance for either an Item or Weapon to appear in the Shop:
However, early rounds guarantee a weapon to appear:
- Waves 1, 2, 3: Guaranteed 2 Weapons + 2 Items.
- Waves 4, 5, 6: Guaranteed 1 Weapon + 3 other purchasables (ie. either a weapons or items).
- Waves 7+: No guarantees.
Item Tags
Characters with "wanted tags" (which are Item Tags that suit their playstyle) have a higher chance to find an item with that tag:
Whenever an item appears in the shop, it has a 5% chance to be selected from an item pool of your tagged items, instead of the regular item pool. This guarantees that the item has one of your character's tags.
- Considering the 65% for a item, the actual chance is: 3.25% per slot in the shop.
Weapons & Classes
When a weapon appears in the Shop (35%), there is a chance to match an owned weapon, or an owned weapon's class (eg. Blade, Unarmed).
- Same weapon chance: 20%
- Considering the 35% for a weapon, the actual chance is: 7%.
- This chance is checked first, taking precedent over the "same weapon class" chance.
- Same weapon class chance: 35% (that are not same weapon)
- Considering the 35% for a weapon, the actual chance is: 12.25%.
- Waves 1-6 also have a bonus chance (see below).
The shops for waves 1-6 also have a bonus chance for the same weapon class. The bonus is higher for earlier waves.
| Wave | 1 | 2 | 3 | 4 | 5 | 6 | ... | 7 - 19 |
|---|---|---|---|---|---|---|---|---|
| % Bonus | 15 | 12.5 | 10 | 7.5 | 5 | 2.5 | ... | - |
| % Bonus + Base (35%) | 50 | 47.5 | 45 | 42.5 | 40 | 37.5 | ... | 35 |
| % Actual Chance † | 17.5 | 16.625 | 15.75 | 14.875 | 14 | 13.125 | ... | 12.25 |
† Considering the 35% chance for a weapon
This bonus allows for a build selection in early game, since the first 3 shops guarantee two weapons, and the next 3 shops guarantee at least one weapon.
Modifiers
Item Cost
Coupon reduces shop prices by -5%, and is the only item that can do this. Shop cost reductions stack additively and the total can be seen in the secondary stats tab. The maximum cost reduction you can have is currently 50% by playing Entrepreneur and having the maximum amount of 5 coupons.
Waves
Harder waves give better shops.
Specifically, each new wave increases the chance for rarer items, as shown in Rarity of Shop Items and Luck above (see "current wave" in the calculations).
Character Specific
Bull is the only character that will not get offered a weapon since it cannot use weapons. It will only get offered items.
Demon is a unique character that buys items with 
Max HP.- Entrepreneur has -25% Items Price buff.
Saver and 
Mutant have +50% Items Price debuff.
Glutton has +25% Items Price debuff.
Ranger Can only purchase Range weapons in the shop.
Gladiator Can only purchase melee weapons in the shop.
Knight Can only purchase melee weapons in the shop, and all weapons offered are Tier 2 or higher.