That's right, you read the topic for today right. I want to talk about mitigating success, why you may want to, and how you can do it. This is a strange and somewhat controversial topic, as basically we're talking about snatching complete victory out of the clutches of your players' hands. However, sometimes it is necessary, and done right it can really spice things up.
Let me start with this. I am not trying to turn your game, or my game, or any game out there into an adversarial game. This isn't about turning a victory into a loss, it is about making it a smaller victory so that the game can progress, tension can rise, and everyone can have more fun. Like all my advice that requires a disclaimer, this is something to break out rarely. Otherwise, you may rob fun and not enhance it.
The Frustration of High Rolls
Sometimes the dice just suck. Anyone who has gamed for a long time can tell you that, and it can be even more frustrating for the GM because consistently high dice rolls can flat out change the full feel of the game and make it into a bad experience as encounters that were carefully balanced to be a challenge are simply wiped out in a few rounds. For example, in a Heavy Gear game I was in once, everyone signed up for a high grit game. People were going to get maimed and killed in this game. However, once it came down to combat, the players' dice just wouldn't stop rolling critical successes. Now, the GM was awesome and rolled with it, and didn't seem too frustrated, but it had to be annoying having the gritty, down and dirty game turn into a cinematic explosion fest on him.
This advice is to help give ways to challenge players when this type of situation comes up.
Sometimes You Can't Do It
The last disclaimer is this. Sometimes you can't do some of these things. Combat is one instance where the dice are going to tell more, so mitigating their success directly is a bad thing. Challenge where you can, and lay off where doing so is just downright unfair.
Save for Half
This is advice I've given elsewhere on here, but the "save for half damage" is nothing new to gaming. It also doesn't have to only be used in combat or with damage. There are lots of situations where the best a player can hope for is to not be in as bad a situation as they were. Leaping to avoid a pit trap, and ending up hanging off the ledge for example. Yes, the player was aiming to clear the pit, and they succeeded. They just didn't succeed all the way. Effectively, there is still some effect from the pit trap.
Now, obviously, this mitigated success shouldn't get the player killed or hurt more. It's not cool to make the round lost to scrambling up the side of the pit ledge be the round that traps the player in the death pit. However, it can make it closer in a more believable fashion.
Choice > Die Roll
A fun way to handle things is to give the player a choice instead of the dice roll. To go back to the pit example, when the player makes the jump, give them a choice. "You can lose the weapon you're holding and make it for sure, or roll and see what happens." If the player choses to lose the weapon in hand, they jump, grab the ledge - but lose their weapon - and pull themselves up safely on the other side. If they make the roll, yes they may succeed, but they also might fail and go down the hole, or lose the weapon anyhow.
This method gets more fun when you get creative with it as well. Don't cost them their gear permanently, but rather just for a few rounds. "Have your sword go sliding away out of hand, but recoverable, or make the roll". Then the player has to recover the item lost, but it is easier to make the choice since it isn't a permanent loss of the item. Just a temporary handicap. The choice puts the tension on the player, and also takes those filthy dice out of the equation briefly. The player is in control of their destiny, and you get to see how they react to this sort of choice. Does the character release his sword to make a jump? Or risk it all to ensure that he doesn't lose his weapon?
Penalty vs. Damage
Here is a scenario I've run into as a GM more times than I can count. Something happens, like a car crash, and the player is getting hurtled through the air. Their very first question? "What do I need to roll to hold on to my weapon?" Now, this is a fair question. Odds are that if your car just blew up, you are about to be in a fight. Also, you as the GM should allow the player a chance to keep their weapon. However, it doesn't have to be dependent on a roll.
For example, one thing I did once was tell the player that he could hold onto the weapon. However, if he was willing to let the weapon go I would give him a bonus (+3 I think it was at the time) to the reflexes roll to reduce the damage from hitting the ground after being ejected from the vehicle. Now, there are two things that are important to this. One, I am not penalizing the player for holding onto his weapon. Two, the player has been given a solid choice here. A good bonus to halve the damage he's about to take, or starting without his favorite weapon in hand. Both are likely to be game changers in the upcoming fight, so it really just comes down to which one he wanted to take. He chose to keep his gun, and then - as luck had it - failed the reflexes save by 2. The extra damage he took almost cost him the character's life too, but they were luckily saved by another PC.
Going back to our friends the dice, it is important to not rob your players of their critical successes. Many systems have ways of handling how successful a roll is, even if it is just "base" versus "amazing". Whenever a player rolls a high level of success, you should give it to them. After all, they earned it with their roll. However, at the same time, that doesn't mean that you can't have lower grades of success also available. Going back to the "save for half" pit jumping situation, it could be that a critical gets the player across without problems, while anything else involves grabbing the ledge or a rope/vine somewhere along the way down. The better the player rolls, the closer to the top they are.
Remember, don't rob them of the success, but don't be afraid to make a success be a bit less - or a bit more dramatic - than the person might have been expecting at the time.
As usual, I'm sure I missed something - or otherwise got lost in my ramblings - along the way here. So, if I missed something, or you want to add a way (or tell a story) of how you did this right, please sound off in the comments below.