Once upon a time I noticed that nearly any fantasy trope would work in an Old West game.
So I made an old-west with magic and motored down the well worn fantasy gaming pathways.
This was GURPS 3e revised.
Luck is an advantage that lets you get two do-overs (three total) to any given roll per real world hour.
One of the players had taken Luck and upon using it, would begin stalling for time. GURPS is not known for speedy play during combat time, so it was relatively simple to burn an hour before his next action came around. But a ten minute round of one second game time was taking an hour because of it.
He had accomplices to help the stalling and it honestly took me several sessions to notice what he was doing.
He picked a fight with three US Cavalry Troopers.
He used his luck forcing me to reroll one of the trooper's shots that would have killed him.
Since it was their action, I demanded he get on with it. The accomplices took out two of the troopers and he rolled a critical success to the vitals of the third...
"Reroll," I tell him.
"Why?" he asks.
"He's got luck, reroll."
"He can't have luck, that's a PLAYER advantage only."
"Really? show me in the book."
There is no rule in the book that so states that Luck is a PC only advantage.
He grudgingly rolls and I take the critical failure as his roll.
He's really fuming now. So I start stalling for time... He notices, but has a glimmer... His luck will roll around before my NPC's. He's gonna win and he knows it.
Thirty minutes after I used my NPC's luck, I stop stalling and it's the NPC's turn. I roll, miss. I roll again, miss. I roll again, critical success to vitals. Roll damage, PC is dead.
PC is in a rage. That's not FAIR! Luck is every HOUR!
Luck, is every hour, true. Extraordinary Luck, on the other hand is every half hour.
The debate about this takes more than half and hour, and the accomplices fail to kill the lucky NPC because of it. More stalling on my part gets him his luck roll back in time to off accomplice one. More stalling and accomplice two fails to end it, yet more stalling and NPC wins the fight.
Rage and hate from all three players.
FuzzyGeff and Standing Bear (an Iowa gaming legend) both step in and explain how they brought this on themselves by abusing the advantage in the first place and didn't seem to mind when everything was going their way.