E21S's Copper upgrade

The mod allows you to upgrade your tools with copper, making copper a more sought after resource. To upgrade a tool, you need to find a structure called a blocked passage, dig it up and find a treasure chest containing a copper rune. Also, to upgrade, you need to melt a copper ingot in a furnace to get molten copper. Using a copper rune and molten copper on a blacksmith's table, you can upgrade any of your tools, making them much more efficient.