Rupee is the second highest tier DivineRPG Overworld material, surpassed only by Bedrock, which requires Rupee Blocks to be crafted. Rupee is a very rare ore, much rarer than Diamond and the 2nd rarest DivineRPG ore in the Overworld. If you want to find Rupee, they are more common between y-levels 4 to 12, but they can spawn at any level below 13. They spawn in veins of 1-3 (mostly in 1). Strip-mining is the most efficient way to find Rupee Ore. One Rupee Ingot is also always dropped by The Eye.
Rupee is used to craft high tier armor, weapons, and tools. Rupee is also a requirement in crafting Shadow Bars and Bedrock. You can also craft a Rupee Shickaxe, by combining all four Rupee tools (Pickaxe, Shovel, Axe, Hoe) together. This functions as all tools combined into one infinitely durable item. As the Shickaxe only requires 9 Rupee Ingots it is recommended to save up and get one rather than the individual tools, as the individual tools do wear out.
Below is a video containing all the recipes that Rupee is used in, made by Lulyhead. All recipes are also listed on the Rupee Ingot page.
Hints & Tips
Rupee Ore is very rare and valuable early in the game so it is not recommended to use them for tools or weapons. The armor, however, can make you invincible to overworld melee mobs and is even useful through all the twilight dimensions. Combine it with Protection IV and you will never have to worry about any sort of melee damage from mobs.
There is a mob called "The Eye" that always drops one Rupee Ingot when killed. However, they hit you with blindness so they are sometimes annoying to kill (but not too difficult). Despite this, they are the best source of Rupee Ingots. A good way to spawn "The Eye" is to make a huge lit room in level 10/7. However, other underground mobs may spawn along with it, such as the Enthralled Dramcryx, Cave Crawler and the Caveclops, which may get in the way (unless you are farming for their drops too).
Rupee Ore is TNT proof, as well as Realmite Ore and Arlemite Ore.