Plunder Rummage is a mod that adds a new mechanic to Minecraft; treasure hunting! I designed the mod to be configurable (highly) and leaving only core mechanics non-optional (treasure maps), as well as making it a mod desirable to those that both enjoy exploring their world, and those who need a reason to! Treasure maps are dropped by some hostile mobs (5% change to drop), and there are three difficulty levels: Easy (always one-stage), Medium (multiple stages of rewards), and Hard (multiple stages with the final stage offering the rewards). 50% of the time a map drops, it will be Easy, 33% of the time it will be Medium, and 17% of the time it will be Hard. Easy maps will only reward easy rewards (those added by .easy.txt files), Medium maps will reward medium (.med.txt files) and easy rewards (easy have their default weight x2). Hard maps will reward all levels of rewards (.hard.txt files), with the items' weights being multiplied by 2 for medium and 3 for easy. Hard rewards are fairly hard to acquire, but they can be a good source for other resources, too.
For all information on this mod, visit this thread.