From Brotato Wiki

Danger Levels

Danger 0
Danger 1
Danger 2
Danger 3
Danger 4
Danger 5

Each level inherits the difficulty increases from level before them.

Danger 0

No Modifiers

Danger 1

New Enemies Appear

Danger 2

Inflation is increased by 5% (needs confirmation). After each wave item prices in shop increased by total inflation. After first wave item prices are increased by 5%. After second wave item prices are increased by 10%. On the last wave item prices are increased by 100%.

Danger 3

Enemies are stronger. Enemies hit 5% more, have 5% more hp, and run 5% faster.

Danger 4

Enemies do not drop materials 5(needs confirmation)% of the time.

Danger 5

On the 20th wave of the run, two bosses spawn instead of one.