From Brotato Wiki
Stats
A random weapon is upgraded when entering a shop. If you have no weapon to upgrade, you gain +2 Armor instead.
Price
120
Limit
1
Unlocked by
Win a run with
Arms Dealer

None
Item
Anvil is an in-game item that can be bought from Shop or can be found in a Crate. Most Items increase the Stats of the player while some of them provide unique effects.
Unique
Anvil is a unique item. Unique items can only be bought or found once per run.
Notes
Anvil will upgrade a random weapon of yours each time you enter a shop. Once there are no weapons to upgrade, it will give you 2 Armor instead.
When acquired on Wildling, your weapons cannot be upgraded above Tier 2 by the Anvil, so Anvil will give you armor instead.
Arms Dealer will lose their weapons first when entering the shop, so will always get the 2 Armor.