The Monkey's Paw

There's a fun little challenge going around Reddit linked to The Adventure Zone called The Ring of the Grammarian. Basically, it's a ring that allows you to craft homebrew spells on-the-spot by mutating a single letter in the spell's title. I had some fun with this about two years ago for the Infinity Hotel setting (almost a year to the date since The Adventure Zone had it in their podcast).

For Example

I've mulled on this before, but this challenge/object/mechanic presents an interesting problem for both the player and the GM to solve: generate a new spell from scratch - probably on the spot, probably without preparation - and not have it be an entirely ineffective downer by default. You're using up a spell slot for the Ring to work, after all. It shouldn't be entirely useless. You're casting a spell - potentially a very precious spell.

And there isn't really any guidance for how to determine exactly how effective this new spell will be. You pretty much just need to wing it. You can kinda eyeball it with the Spell Level and such, perhaps re-skin the mechanic with a new type of damage or modify the base spell's parameters. Somewhere along the way, though, you'll need to determine how this affects the chances. You'll need to move the odds somewhere along the this-automatically-fails to this-automatically-succeeds continuum (with all sorts of advantages, disadvantages, bonuses, and penalties to dice rolls betwixt). To assist in this measure, I'll illustrate what I call The Monkey's Paw Principle. (Named, of course, for the story we are all somewhat familiar with.)

The Monkey's Paw Principle is this:

Independent of other variables and controlled for resource expenditure, the more absurdly specific a resource is, the less risk it should entail.

It kinda seems like a no-brainer though, right? Specific solution > Non-specific solution. But you would not believe how many times I've played in games where this has been ignored, primarily as an lazy excuse to reign in the unpredictability of homebrew content.

((Side Note: It's applicable to more than spells. It should, for instance, apply to any sort of tool (a grappling hook, for instance), but I'll focus on spells for the moment because their importance as a limited resource is obvious.))

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I'd like to illustrate this with a couple of D&D spell staples: Jump, Burning Hands, Magic Missile, and Wish. Then a couple of Grammarian / paronym examples.

Jump is a fairly absurdly specific spell. You cast it, you can jump higher. That's all it really does. Totally useless in scenarios that don't involve jumping. It is the juicer of spells: it can juice plenty of things, but unless you're throwing it at something it's just gonna make juice.

Going by the Monkey's Paw Principle, if a player actually spends the precious resources on the Jump spell - a resource which could be spent on the far more versatile Burning Hands - and their problem involves jumping, then they damn sure should have a heck of an advantage on that task. You probably shouldn't even roll, lest other factors are significantly getting in the way (hazards, traps, goalkeeping baddies, etc.).

Burning Hands, by contrast, is a very versatile spell. Fire shoots out of your hands. There is a wide arrangement of scenarios that fire can solve: burning dudes, starting brush fires, creating steam smokescreens, heating giant tea kettles, impressing your fire elemental boyfriend, the list goes on and on.

Source

But because of its wide use of applications and its obvious and plentiful uses, using Burning Hands should generally entail more risk during its course of burning things than Jump entails in its jumping. Baddies make Saves, fires sometimes don't catch, and your fire elemental boyfriend isn't always easily impressed. Jump, however, should almost always solve your jumping problems.

To an extreme, Magic Missile is a hyper-specific spell with near-total inviolability. The only way it's avoided is with specific counters. It is the banana holder of spells: it can hold bananas, and that's it, but it does it perfectly virtually all the time. You deal damage to a living creature. It's guaranteed. Roll your low-uncertainty damage. So hyper specific that there's no uncertainty with how it works at all.

(Wish, paradoxically, is an incredibly unspecific, versatile spell that includes the Monkey's Paw Principle embedded within it automatically. The more absurdly specific your Wish, the less risky it should be.)

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Let's try and apply these to new spells generated by the Grammarian Ring or a Paromancer:

Magic Mouth -> Magic Moth
Disguise Self -> Disguise Shelf

Your player decides to cast the spell Magic Moth. Okay... What the hell does a Magic Moth do? Well... It's a moth and it's magic. It could do virtually anything, provided it has some quintessential mothiness or moth flavor thrown in.

Close enough.

Maybe it's like a Butterfree and it spreads sleep spores around willy-nilly. Not unreasonable - just like the Sleep spell, but maybe increase the HD to match its 2nd Level Spell Slot use. Maybe the Magic Moth flocks to tricksters, liars, or traitors, because that's what magic moths do in your setting. Maybe it feeds on eyeball juices and radiates Color Spray all the time.

You've got tons and tons of potential options for what a Magic Moth does, so how do you determine its effectiveness? Well, I propose that this would depend on how absurdly useful the Moth and Magic parts of this spell are within the present situation. Trying to distract a Giant Magic Bat with giant magic food? Magic Moth is 100% effective. No rolls needed. Trying to distract some street thugs? Well, unless they're specifically afraid of moths or worship the Moth God, maybe you roll for its effectiveness, standard check. Trying to force open a door? Well... What parts of Magic and Moth are relevant or specific to door-opening? Magic? Sure. Moth? Not much. Completely ineffective.

Your player decides to cast Disguise Shelf. Why on earth did they decide to do that? Was it to magically disguise a shelf?

No? Well what good could that possibly be? The spell's title is pretty self-evident that it's about disguising shelves.

Yes? Well then that Disguise Shelf spell better be the most damned effective spell at disguising shelves you've ever seen. Whatever counteracts that Disguise Shelf should be at least as absurd as the likelihood of Disguise Shelf being used effectively. Otherwise what was the point of that creativity?

Nobody will ever discover where you keep your porn...

Hopefully, this gives some insight as to how effective absurd homebrew content should be. It won't help you come up with mechanics, but it should give you an idea for how strong these new mechanics should be.