Rainbow shields, damage of the gaps, prescribed and ad lib skills

In a lot of RPGs, players have skills, stats or whatever you want to call them that are well defined. Things like Medicine, Nature, Insight, etc. in D&D, or Occult, Drive, Larceny in Chronicles of Darkness. Then there are some games that are more flexible where the players are asked to fill in their own ad lib skills and stats - games like DOGS, Godbound or Chuubo's Marvelous Wish-Granting Engine, where you can pretty much write anything in as a stat - "Memory of my dead brother", "Fastest gun in the west", or "underwater basket weaving".

The problem with the latter is the fuzzy boarders each such statement creates about when a given skill should be used, when it shouldn't apply, and avoiding skills that are too broad or too narrow.

Broad vs narrow skill applications

There are RPGs out there that like to break skills down to minutia. In Burning Wheel there are a lot of skills - under Carpentry alone you have Fence Building, Ditch Digging, Carving, Carpentry, Rude Carpentry, Cooping (making barrels), Boatwright, Shipwright, Cartwright and a few more. This creates a sort of Air-Breathing Mermaid Problem, where the game basically forces the GM's hand to say "sorry, you only have Carpentry, you can't carve and decorate what you build and you can't seem to know how to make a barrel". It can also create traps if characters specialise in some skill that doesn't come up that often - "I know you're a master Cooper, but no matter how great that barrel you make will be it still won't help you sail the sea, you need Boatwright for that".

You can run into similar problems in games where players can define their own ad lib skills, but those also sway in the other direction - they can be too broadly applicable. You could have players put ranks into "underwater basket weaving" only for that to come in handy once or twice in the entire game, while someone else makes a stat called "fast" and they want to use it all the time - "I shoot him, but like, fast", "I read, fast", "I sleep, fast", etc. The boarders where such player-defined skills apply are fuzzy - you can't really tell them that because there is some other skill that also works for the situation theirs might not apply. Moreover, players will often skew the problem in their favour just so they can use their best skills - "I make a basket under water and it's so well crafted I can use it as a raft with a sail to navigate the rough sea. It's all baskets, just different shapes."

City of Mist tried addressing this problem by classifying its tags into "specific" and "broad". Most tags on a character sheet should be specific - only letting the character use them in specific, limited scenarios. One tag could be broad - applicable in wide variety of situations.

Rainbow shields and damage of the gaps

While playing Exalted / Godbound with my group we would often reference a "rainbow shield" defence - a power to negate any kind of incoming damage, no matter whether it's physical, magical, fire, electricity, etc. A system that would allow for such widely-applicable defence to exist wouldn't be too fun to play really. Exalted 2nd edition suffered from something like that from what I heard - someone created an optimal way of playing the game called "paranoia combat" that's all about using perfect defence against the high-lethality rocket-tag and outlast your opponent.

In our first round of playing Godbound we ended up being too generous with defences, letting the players counter most attacks with most power sets - "I use Artifice to instantly build a wall around myself to deflect the incoming blow!". As we later found out, Godbound was not intended to work like that - any given Word should only counter a very narrow range of powers that are thematically linked to it. You could use Sea to counter a Fire power, but not say, Sword.

However, the game had a different problem, one which I'll call "damage of the gaps". The system did not have a specified, finite list of damage types. A number of powers did either give you things you could be immune to, or let you specify said immunity - for example, if you had the Word of Fire you had "an invincible defence against flame and smoke". But since "smoke" was ill-defined, we had an argument about whether that Word would apply against chemical fumes and poisonous gasses. Similarly, in the Ancalia expansion introduced an Incendiary Court - fire-golem-like creatures from outside of reality that while clearly having fire-based attacks nonetheless came with a note that their "flaming powers are not wholly of natural fire, and so enemies with invincible defences against fire still take half damage from them". This was probably to prevent players circumventing a big boss fight entirely, but still felt like a weird way to make a power less useful.

In a similar vein you could start splitting hairs on many things - if you are immune to mental attacks and someone uses music or mean words on you, does that count? Where does mental damage end and emotional damage begin? Is a psychic blow magic, mental or physical? Is a laser attack fire, sunlight, or neither? Can I make some very snowflake-y Word that has its own damage type that none of the statted enemies have defence against?

Because the game had no finite and well-defined list of damage types, you either have to make one yourself before the game starts, or possibly have to argue about this kind of damage of the gaps...

Conclusions

While being able to get creative with skills and powers can be fun, having things that are well-defined and concise can help everyone at the table know when something is applicable and avoid the problems of things being either too narrowly or too broadly useful.