Breaking the Rules
I had a teacher in elementary school who taught us about creative writing, saying, “You aren’t allowed to break the rules of language until you fully understand how to use them.” This is true for any art form, including the creation and balancing of roleplaying game campaigns. It’s important to understand how the rules of the game work together, because it’s critically important to good DMing that you also break them.
The rule books usually help DMs with understanding how to balance the game; how much gold players should have, how strong the monsters should be, and how much weight someone can carry based on their stats. These fundamental parts of the game are necessary, but because they’re ever-present, there is nothing special or memorable about them. What is special, is when someone gets the opportunity from the DM to unbalance the game. It’s in these cases where memories are created, and favourite characters are developed. It’s not the only way to accomplish it, but adding a little extra power to a player is a surefire way to have a player recounting their experiences to others later with excitement.
The mysterious Starfolk, Dell, managed to secretly complete a contract on the side, earning her, and her alone, an extra 50 000 gp. Sven was gifted a Gnomish Chainsaw; a weapon so big and unwieldy it took a minotaur like him to use it, which he did, dealing 3d12 damage with a simple touch attack. Captain Madrick managed to use the final wish on his Luck Blade to grant himself blindsight out to 120 ft, meaning he was never able to be caught unaware ever again. All of these examples feel like they would throw off the balance of the game. However, if a DM manages to incorporate epic power spikes like these, without upsetting the other players or the “feel” of the setting, and can keep the story flowing naturally, they will have created more than just another game session; they’ll have created a story that people will want to share with others long after the game is done.
The reason I say that you need to understand fully how the rules work is because you are going to rely on those rules to maintain a fun, balanced experience for the rest of the party after breaking a rule. When giving something that sounds amazing, you need to consider what it actually is you’re giving them, and what rules it must abide by. In my examples, 50 000 gp is more often than not either going to be used to buy one, big awesome item, or be held onto until something really juicy comes up. If that one item suddenly becomes a key story hook for the whole party, it doesn’t feel like you’ve given one player something only they can enjoy. A player who saves the money is just asking for the DM to create something that caters to their character, and their campaign; this gives you all the opportunity you need to reign in control, by making an item that really fits your story. In both cases 50 000 gp is actually just a story hook.
A chainsaw seems like a terrifying weapon, until you consider the limitations you put on it; I made mine so that it was entirely technological, and could not be enchanted. This made it useless against ghosts, not as effective against creatures with resistance to non-magic attacks, but still destroyed those who had no immunities. It has never broken a game, in my experience, to give single character an attack that deals tons of damage. If it ever did, then again, this item becomes part of some storyline, and may end up in it being sacrificed, passed on to a grander purpose, etc. But not before I give the minotaur a couple dozen goblins to slay.
Finally, with blindsight, it was simply a matter of considering that I had reached a certain point in the campaign earlier than usual. What I mean by this is that every adventuring party will eventually have plane shift. They will eventually be able to fly. They will eventually have a couple ways to heal the entire party at once. By allowing one character to avoid being snuck up on, I moved what would likely be an eventuality to an earlier part of the game. But again, by knowing the limitations of the power you give, you leave it open for opportunities to exploit it. Just don’t do that right away; you always want to give the players a couple chances to really flex those magical abilities before showing them the flaws.