So with this, you can sometimes get an uber-rare drop (like 1 in 80mil) from just about any mob. When you use it (it looks like a scroll), you can choose one of your stats: either STR, DEX, INT, or VIT. That skill gets a permanent +3, but one of your other three (randomly determined) gets a permanent -2. So you can get uber lucky (for instance, choosing INT as a mage and getting a STR penalty) or uber unlucky (choosing STR as a Ranger and getting DEX penalty).
There could also be another variant, that causes a permanent -4 to all four stats (STR, DEX, INT, and VIT), but allows you an extra 3 skill points. This variant has a 1 in 1 billion chance to drop instead of the stat variant whenever the stat variant drops.
Stat Variant Drop Chance: 1 in 80,000,000 from any mob
Skill Variant Drop Chance: 1 in 80,000,000,000,000 from any mob (1 in 1 billion from 1 in 80 million)