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Simple 5E Sub-Systems for DMs in a Hurry

How do we embrace fun, new gaming opportunities in 5E without overly complex sub-systems? By asking three questions.

Zipperon Disney asked on Twitter:

I think most homebrew alchemy systems for #DnD are overly taxing on the DM and time at the table. Worldbuild magic ingredients, Gather them, keep track of their potential effects, resolve brewing… Anyone have a simple alchemy system?

His post highlights a real problem in the 5E space: fun gaming opportunities solved with overly complex sub-systems. Take alchemy from the above post for example. As DMs, we want the experience to feel like more than a simple ability check. But we also want to focus on the fun and not introduce needlessly complex game mechanics. Where’s that balance?

When creating a sub-system for D&D 5E, I think we can benefit from breaking it down into three guiding questions:

  1. What problem is this solving?
  2. What mechanics already exist that can be reused?
  3. Where can I introduce the core mechanic?

What Problem is This Solving?

The main problem is usually something like a player in my game wants to explore something that doesn’t have a set of explicit mechanics. I don’t like problem statements like my world doesn’t have a set of alchemy mechanics because I don’t think your world needs one until a player needs one.

We can build a powerful problem statement by borrowing concepts like user stories. When my team builds software, we group each slice of work into a “story” that’s framed like this:

As ____, I want ____ so that ____.

It’s powerful because it clarifies who, what, and why. Understanding the problem you’re setting out to solve will help guide the rest of your creation.

For my example, the problem is a player in my game wants their character to practice alchemy so that they can make potions.

What Mechanics Can I Reuse?

A dozen or more professional designers with far more resources and experience than any of us have built and refined 5E over the last near decade. It’s the most popular tabletop roleplaying game in the world. If I can reuse anything that already exists, I’m going to.

Reusing mechanics provides something refined and familiar to our players. It can help your sub-system feel like a natural part of the game. Some sub-systems are incredibly complex. When they come into play, it feels like you need to context switch away from 5E altogether. That’s when a sub-system has gone too far.

For my example, I think spells and downtime activities might have mechanics I can reuse. Some spells require a material component and one can imagine that brewing potions should as well. After 2nd or 3rd level, I don’t think that tracking material components adds much fun to the game. Luckily, spells can use a spellcasting focus (for non-valued components) instead. Let’s use that.

Downtime activities in Xanathar’s Guide to Everything has a section on brewing Potions of Healing. It has a time and cost associated with each type of potion. I like the idea of abstracting ingredients or material components into a flat cost. Let’s replace the spellcasting focus with that.

Where Can I Introduce the Core Mechanic?

By “core mechanic” I’m talking about the following:

  1. Describe what you want to accomplish.
  2. Set an appropriate DC for an ability check.
  3. Roll 1d20 and add the appropriate modifiers.

This is the beating heart of 5E mechanics. It’s familiar. It’s fun. In my experience, players want to roll dice. While it might be tempting to would-be game designers, 5E isn’t the best place to experiment with wildly unfamiliar dice mechanics. Rolling 3d12 and 1d8 to resolve an action will feel strange and hard to remember. That’s why I like to introduce the core mechanic in my sub-systems.

Let’s wrap up our example of an alchemy for brewing potions sub-system.

Colored potion bottles

Alchemy for Brewing Potions Sub-System for 5E

To practice alchemy and brew potions, the character must:

  1. Be proficient with artisan’s tools (alchemist’s supplies).
  2. Acquire the recipe for the desired potion (potion of healing, oil of etherealness, etc).
  3. Pay the cost of ingredients.
  4. Attempt an Arcana check (DC determined by the Potion Brewing table below).

Potion Brewing Table

Potion RarityDCCost
Very Rare2510,000gp

That’s it! A simple sub-system that solves our problem, reflects existing mechanics, and implements the core mechanic of 5E. Another benefit of a simple system is that it’s easy to change if it falls apart in play. You’re not rewriting a complex system. You’re tweaking a simple one.

To recap, we can benefit from asking three questions before creating a new sub-system for 5E. What problem is this solving? What mechanics already exist that can be reused? Where can I introduce the core mechanic? And that’s it. A way to create simple 5E sub-systems for DMs in a hurry.