From Brotato Wiki
Item
Dangerous Bunny 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.
Dangerous Bunny
Dangerous Bunny gives you 1 additional free reroll in the Shop for each one you have. The item count is limited to 3 per run (which would give 3 free rerolls in each shop).
The free rerolls always happen before the regular rerolls, and do not increase the reroll cost for subsequent (regular) rerolls.
When a Dangerous Bunny is purchased, the free reroll is granted immediately and can be used in the current shop. This will not increase the cost of later rerolls for this shop.
Also see Shop Rerolling.
The game displays how many materials were saved by the Dangerous Bunnies for the current run in the item tooltip. This information does not take into account the material cost of the Dangerous Bunnies themselves (if they were purchased, and not found in a crate).