The best feature of a pen-and-paper roleplaying game, over an MMO or other more structured game, is the ability to be creative. But DMs vary significantly in how creative they allow their players to be, often through concerns about the letter of the rules, or creating imbalances. Here’s some thoughts on how to open things up a bit without breaking your game.
Rule of Cool
A player asked me today if he could use the spell Control Water to climb up a wall. I thought about this a bit, read through the description a few times, and then eventually realised I was taking the wrong approach.
Swimming up the outside of a castle? That’s kinda cool. I shouldn’t be trying to stop this, I should be trying to enable it. This is creative use of an interesting spell: I want to reward this kind of thinking.
Tell the players that cool ideas are rewarded, and then do it. If a Rogue tries to vault off the banister of a staircase to get more momentum on an attack, let them, and then give them Advantage or something if they succeed. Give positive reinforcement.
Shut down ideas that aren’t cool, and make it clear to the players why you’re rejecting the ideas. A few of my players had a long discussion about whether they could cut off and eat parts of the Druid when he was in animal form. I don’t care whether that’s allowed by the rules or not, it’s absurd and I don’t want that in my game. :-/ Your mileage may vary.
Offset bonuses with difficulties
To try to maintain balance, you shouldn’t give anything for free. Swimming vertically in Control Water? Athletics check. Trying to get Advantage by leaping off a banister? Acrobatics check.
Generally skill checks are a really good way of offsetting these kinds of things. Everyone’s got skills, and everyone likes using them, so give them the chance. Depending on the level of power involved, skills might not be enough, and you could look at how spells are balanced for ideas: long time to cast / set up, expensive components, and Concentration. You want to use a large bed as a boat? Sure, but it’ll take you a while to drag it down the stairs (and yes, this from an actual session).
Compare the power level
Especially when looking at the versatility of spells, you should compare the power of the spell to others. A level 1 spell shouldn’t end up as powerful as level 2+, and you shouldn’t be able to duplicate the effects of other spells, particularly from different classes.
Consider the previous example of using Control Water to climb a castle. It’s a level 4 Cleric spell. Wizards get Levitate as level 2, and Fly as level 3. So we’re using a higher spell slot to situationally replicate the capability of lower-level spells from another class. I think that’s fine: level 4 slots are definitely more valuable, and you need the water and a surface for it to run up.
As a counter-example, I had players try to argue that they could make a Minor Illusion move, by rapidly re-casting it, essentially duplicating the power of higher-level Illusions. That’s not okay, and would definitely cause balance issues.
Prepare for unforeseen consequences
My players got their hands on a scroll that could open a gateway to the Elemental Plane of Fire. I intended on it being one use only, but they tried to use it again and I thought I could make it more interesting.
The portal opened, a fire elemental attacked them, they killed it, they closed it. They found a lich’s phylactery, so they opened the portal, and threw it in. They needed to dispose of some bodies, so they chucked them through the portal.
However, with each opening, I hinted that the creatures on the other side are completely capable and interested in coming through. They eventually got to the point where they will only open the portal in an absolute emergency, because they are quite fairly terrified of an invasion of the Material Plane by an army of Efreet and Salamanders.
By giving in-character reasons why they shouldn’t keep doing it, the whole process was self-limiting and led to more plot. A great solution for everyone.
Sometimes, you can’t work out a way of restricting something, but you want to allow it anyway. It’s just too cool. The idea is fantastic. But it’ll break the game.
Allow it once. Just once. Ask the players not to do it again, and preferably rely on an out-of-character agreement to enforce this. If they do try it again, it won’t work, and you can make that clear.
In this way, you can have something crazy happen (like dropping a whale on someone) without completely breaking the game (characters using whales as their primary weapon henceforth).
Sometimes, you just have to say “no”
I’ve seen advice on DMing to never say “no”, but rather say, “yes, but…”. That’s a good guideline, but really you have to remember that sometimes “no” is the right answer.
The DM has the responsibility to manage the game and make it fun for everyone. Sometimes, you just have to say “no” and move on.