Are there issues about making up own skills, when commonly used?

Question

When using ability checks I often think about whether knowledge of something fits into one of the skills.

Is it a nature-, religion- or just a plain intelligence check to recall knowledge about creatures of other planes or undead? When talking about laws, what kind of check would it be? Probably plain intelligence.

The problem occurs when one of the characters is a demon hunter or a lawyer by background. There is as far as I can see no written rule which lets you get proficiency in such checks.

Do you have experience in adding own skills and let players get proficiency in them? Are there problems coming with it?

When thinking about a demon hunter and giving him the "demon lore" skill (or comparable) it would also give him proficiency for checks to recognize demons and recall their abilities, but might be to a too edge case skill. Giving him something like "Monster/Creature Lore" it might be too widespread for the character.

Answer 1

Most of the time, custom skills (unless they're super common for a given setting) are going to be a trap option for your players. They won't be useful very often when compared to the less specific default skills built in to the game, which tend to be quite broad in their application for a standard D&D style fantasy game.

As an alternative, you might consider taking the character's background into account when calling for checks related to such matters. So if the character is a demon hunter give them their proficiency bonus when making Intelligence (Whatever Skill Is Relevant) checks related to Demons. You'll need to make sure your players aren't taking advantage of things by giving themselves the I Know Everything About Everything style background, but if it's not abused it can make the players feel like their back story matters.

Answer 2

Yes I have experience with this: it was called D&D 3.x

In that system the array of skills was absolutely ridiculous and at mid to high levels, because it lacked the bounded accuracy of 5e, if you had a skill you succeeded and if you didn't you failed.

Its a bad idea. PCs in 5e have only the proficiencies (they are not called skills) they start with (unless using the feats variant) and the more you create new proficiencies, the less value each one has. You could compensate by allowing extra proficiencies as part of backgrounds, classes or races but you are just making a rod for your own back.

The design ethos of 5e is to have a very small list of very broad skills. DMs & players should interpret them in a very liberal way - if there is a plausible reason why a given skill applies then it applies. If there is a plausible reason that 2, 3 or more skills apply then they apply.

For your examples:

• creatures of other planes: Arcarna, History, Nature, Religion are all immediately applicable. Investigation could be used if the person had access to research materials, Survival could apply if the person was familiar with other planes.

• undead Arcarna, History, Nature, Religion are all immediately applicable. Investigation could be used if the person had access to research materials.

• laws History is immediately applicable, Arcarna and Religion if considering laws governing magic and worship, Investigation if the person had access to research materials, Insight and Survival are both applicable if the person can observe citizens obeying the laws, Deception if observing people breaking the laws.

These are just off the top of my head and are not closed lists - if a player can come up with a plausible reason at my table then they get the proficiency.

"Can I use an Intelligence (Agility) to learn something about the ape-like demon that is climbing with great agility?" "Yes, you studied Barlgura (MM p.56) as part of you gymnastics training ..."

Answer 3

There's an official variant rule for this.

Have a look in the Dungeon Master's Guide, page 264, "Background Proficiency":

... a character can add his or her proficiency bonus to any ability check to which the character's prior training and experience (reflected in the character's background) reasonably applies. The DM is the ultimate judge of whether the character's background applies.

...

This simple system relies heavily on players developing their characters’ histories. Don’t let it result in endless debates about whether a character's proficiency bonus applies in a given situation. Unless a player's attempt to explain the relevance of the character’s background makes everyone else at the table roll their eyes at its absurdity go ahead and reward the player for making the effort.

So you would decide on a case-by-case basis on whether a character would add their proficiency bonus to an ability check. For example, if your lawyer PC encountered a legal document and wanted to find a loophole, they'd add their proficiency bonus to the roll, because of their background.

I use this system myself with a group that's running Out of the Abyss. I have found it very straightforward and encountered no real problems. For example, our paladin has a background as a reformed thief and brigand. Thus, she gets to add her proficiency bonus to any check where it might reasonably apply. On the other hand, she won't be adding her proficiency bonus to things like identifying demons or religious rituals.

This is also much easier to do in 5th edition than e.g. 3rd edition because the proficiency bonus is simply a flat bonus, and not e.g. a complicated system of skill points.

I also find the background skills variant a bit more "common sense"; why would a fast talking rogue from the street be better at bluffing their way past a university committee than the wizard who has spent their life in them?

Answer 4

A point worth pondering: Ability checks don't have to be hard bound by a rule.

The problem you present is a great opportunity as a DM to adapt and improvise to apply what makes the most sense to you to a given situation. Guiding principle is Rulings over Rules.

... play is fluid and flexible, adapting to the circumstances of the adventure.

Law? You could use either Wisdom or Intelligence as the ability check. Roll only if it matters, otherwise role-play it out and try to apply the ability the player(s) in question are using. The one thing I learned over the years as a DM is "don't try to shoehorn everything into a roll or a rule."

Related to that is, if you are on uncertain ground, use a roll with whatever makes sense to you as the criterion, make a ruling, and play on!

Why do I say this?

Long before this kind of check was formalized in any rule, we used something like this to assess how likely someone was to succeed at "something" that wasn't covered by a clear rule.

"Roll a d20, and if you score your (int/dex/con) or less you succeed, otherwise not."

The DM would add or subtract a modifier based on circumstance. Advantage/Disadvantage is based on circumstance in D&D 5e(p. 239-40, DMG)

Around the time of AD&D 2e, that approach became formally presented in the rules in the non-proficiency and proficiency skill checks, and that got further detail in 3e.

You don't need a rule, as you the DM are the Master of Rules (DMG page 5).

The rules don't account for every possible situation.

What you need is to look at a situation, and see what makes the most sense to you, the world you are all in, and the players, to resolve a question or challenge.

Answer 5

What you want is already exists in the game.

The description of an Intelligence (Arcana) check says it "measures your ability to recall lore about spells, magic items, eldritch symbols, magical traditions, the planes of existence, and the inhabitants of those planes." There's your demons.

Now, for knowledge about the law.

Does your campaign take place in a democratic society? If not, there is no law as we would understand it today. There is only the will of the sovereign. Knowledge of the will of the sovereign is covered by the courtesan background feature. The giving of significant decrees by the sovereign would also be historical matters, thus covered by Intelligence (history).

Your campaign does take place in a democracy? Under Other Intelligence checks, it mentions "Recall lore about a craft or trade". The craft or trade in this case would be lawyer. This is a plain intelligence check. But you want a player to be able to be especially good with this type of knowledge. This should be covered by the background feature of the sage, as understanding the intricacies of such laws would be constant research. The passing of significant laws would be historical matters as well.

PS, I noticed a comment you made saying that you wouldn't go to a historian for legal advice. This may be wise, but you absolutely can go to a lawyer with questions of history, as they're required to study a lot of it. The skill is appropriate.