[Kromm]

Two campaigns ago (fantasy): The player of a legionary officer decided that actually being a good officer would be more interesting than the hackneyed RPG approach of "Rah! Me good at fight! Me general!" For the first couple of years of gaming, it was mostly color – and, this being GURPS, a point-soak. When the scope of the campaign grew more sweeping, though, and he started to lead troops in action, he turned easy victories into zero-casualty cakewalks, even matches into easy victories, meat-grinders into victories with acceptable losses, and even what should have been tragic last stands into hard-won victories. It fit the campaign's tenor for sure, but it definitely accelerated the endgame and changed the aftermath from "Good has prevailed, but at what cost?" to "A new golden age for the forces of Good!"

One campaign ago (espionage/technothriller): The player of a medic for a team of secret agents really went to town on the Housekeeping skill (more GURPS). Again, this was color at first: "She worked as a maid to make ends meet after fleeing Chechnya." But the player wanted to use the skill to "clean" after messy ops, and I allowed it. By the end of the campaign, I believe that was her highest skill and one of the highest skill levels on the squad. Even at considerable penalties, she would use it – in conjunction with her medical skills – to wipe traces of things like break-ins and assassinations so thoroughly that the group more often than not acted with impunity. This resulted in the campaign changing from a gritty post-Cold War spy drama to something more akin to a story about modern-day ninjas.

I should note that I pretty much invite this kind of thing. As the GM, it's part of my fun to be surprised occasionally. It's easy for me to surprise the players. It's much harder for them to surprise me, which is why I love it when they do!