A good example of a really terrible RNG is in Monster Hunter 3 Ultimate, and maybe others. Not only it is completely exploitable for better loot, it also gave

A good example of a really terrible RNG is in Monster Hunter 3 Ultimate, and maybe others. Not only it is completely exploitable for better loot, it also gave rise to "charm table". Some items have randomly generated statistics, and depending on your initial seed (stored in the game save!), there is a limited number of items you can get, and if you are unlucky, you may have a "cursed table", which is effectively a RNG with a really short period, meaning you will never get the best rolls. Not game breaking, but bad for high level play.