I used to play a 'Fantasy Hero' campaign (Hero Gaming System - they used it for several genres). The combat rules feature a -5 penalty for non-proficient weapons. And also allows you to buy bonuses ("levels") with special effects, limited applicability restrictions, etc.
There was a character who had a +10 bonus, only for purposes of negating penalties. Between non-proficiency penalties, range penalties, and penalties on throwing unbalanced and non-aerodynamic objects, it was almost fully applicable almost all the time, if she chose to act in ways that used it. It gave her an astonishingly free and flexible style of play. She was quite dangerous, and could almost always do something highly effective no matter what the circumstances. Picking up and throwing a random rock was a terrifying move when she did it.
In context it was supposed to be the manifestation or result of some enchantment or prophecy relating to a 'perfect warrior' that had been focused on her at a shrine to the champions of her nation, and went with a Holy Mission to free any of her people who came under the yoke of slavery. She was actually quite dangerous, in that it was almost impossible to meaningfully 'disarm' her.