One of the most important topics of game design (to me) when it comes to TTRPGs is progression. How do my player's characters progress in the game. How do they get "stronger"? This decision can have wildly different effects on the feel of the game. There are a ton of different systems out there but I like to try to boil them down into two categories: Vertical and Horizontal.

These categories are not binary, more of a spectrum. All games I've played seem to have a bit of both, leaning more towards one side but still influenced by the other.

Quick preface - this is me rambling about what I think all this stuff means. If there are strict definitions elsewhere, or I'm completely off the mark, I apologize. Just spewing nonsense here.

Vertical Progression

Vertical progression is when a player "levels up", or in some way grows stronger and more powerful overtime. A great example would be an MMORPG such as World of Warcraft. You start at level 1 with a basic staff, smacking bats in a cave. Then, eventually, you reach max level and summon meteors from the heavens to destroy your universe-ending villains. Dungeons & Dragons has a similar vibe. You start your game with a sword and shield, worried that a stray arrow from the group of goblins you're fighting can end your adventure at any moment. After a few sessions , you're slinging Fireballs, dealing huge 8D6 damage to all enemies caught in your blast. You're catching arrows midair and throwing them back at your enemies faster than they were shot from the bow.

The point of vertical progression is to constantly get stronger and more specialized. You start as a simple mage, growing into an Archwizard capable of controlling time and pulling at the fabric of the weave to make anything you wish come true (quite literally with the Wish spell). This adds a very clear path for your players with very tangible goals. Leveling up is a great motivator to continue the story/adventure because the players know, no matter what happens, they will be closer to their next goal, spell, ability, etc.

This progression system is awesome. Easy(ish) to design around not only for player character progression, but also NPC and World progression. Making a monster with a lot of cool abilities and high damaging spells is easy because you can just balance around an ideal level the party should be at when they encounter it. In D&D, this is referred to as Challenge Rating (CR). For example, a Wyvern is a CR6 creature. This means that, generally, a group of 4-5 level 6 characters should have a decently challenging fight.

The other side of this "always gaining power" coin is that, once you have outgrown your previous challenging content, it is no longer relevant. So, while you can always go explore the 'next zone' or gain the new high level spell, the old stuff just seems to fall to the wayside, or become so trivial it no longer matters. An extreme example of this would be the anime Dragonball Z. A villain comes, is so powerful the protagonists have to level up some way, then they defeat the villain. Process repeats (over many... many... many episodes). This is my own experience but in games like this, the world starts off large, unexplored, and full of wonder. However, when you finally reach the higher levels, the world shrinks and you are somewhat delegated to areas that fit your current level of power. I suppose you're also delegated to a certain area while you are weak as well, but the list of "I can't wait to go there or do that' becomes smaller and smaller as you go on.

Perhaps this is for the best. We all know that campaigns very rarely reach their end goal or have an actual satisfying finish. Maybe it's good to have a story that you progress through until the BBEG, defeat the enemy, and call it a day - start over in a new campaign.

Horizontal Progress

So, this one is a bit more nebulous to describe but I'll do my best. Horizontal progression is when your character doesn't necessarily get stronger but instead, more capable. An example of this would be a Metroidvania type game. Sure, you may gain some more health or a stronger weapon along the way, but normally your 'power ups' are things to let you move around the world more freely, or deal specific damage to a certain creature. The MMORPG Guild Wars 2 has a mix of these. There is definitely a level system, and you want to reach max level to do the main content of the game. However, the game has had 2 (3?) expansions now where the level does not increase. The expansions, rather than adding higher levels and more deadly enemies, adds new systems to progress your character through. An example would be the ability to glide on air currents. Most content can be traveled to without a glider, but the glider in most cases makes it easier to reach and, in some other cases, able to reach exclusive areas.

I can't really think of an example of this in a TTRPG but please let me know if you've seen this!

What I like about these types of system is it feels a bit more 'sandboxy'. You kind of carve your own path and decide what you want to level up in. This is not a strict rule, but from my experience I've noticed these games follow a path of 'you can go wherever you want, but getting X item or Y ability will make this place easier/better/more lucrative/etc etc". I like having this openness. As I said before, this isn't a binary decision and absolutely has both sides of the spectrum present. Even a game like The Legend of Zelda has power progression in Hearts (more health). However, this doesn't make the content any easier, just more forgivable. This means that player skill has more of a factor. You can't just power through anything once you've gained enough power, you have to still use the right tools for the job.

I like this system the most. I do think it's harder to design for. Number tuning becomes less of a tool for the designer because you can't just make the content harder by doing more damage. You have to add more mechanical puzzles to stop players from plowing through content. Using Legend of Zelda as an example again, you can only access certain areas if you have a bomb to blow open the entrance. This adds some degree of 'exclusive contents' for players gaining items throughout the game, but the benefit here is it doesn't invalidate previous content. All enemies can hurt you, you just might live through more attacks. In some vertical games, an enemy might not even be able to strike you any longer, they are just too low level to even deal damage.

The negative to this system is its very player driven. The players have to kind of set their own goals on what they want to accomplish. This can be hard for DMs who have players that are just kind of there to play through a story rather than crafting their own. A west marches style campaign fits this design well (albeit still wrapped in a vertical system such as D&D) because it allows the players to pick their goals and create their own adventure. Also, having a more open world might have players feeling lost if they don't know what to expect from each area. Lastly, vertical progression allows you to hyper-specialize in really cool things, unlocking amazing spells or abilities. Horizontal usually leads to more 'Jack-of-all-Trades" type of characters. This is normally preference but it can be hard to find a group that has all the same preference.

Reward System

The reason why I think this is such a big deal when it comes to designing an RPG is because it defines the reward system, which in turn, informs the players decisions. If the best way to gain experience in a game is to fight monsters, then the game is normally designed around becoming better at fighting monsters. If you haven't noticed, most of 5th Edition Dungeons & Dragons spells, abilities, and classes are almost always revolved around becoming better in combat. More damage, more spells, more enemies to be hit at once. A lot of people love this. They just want to roll dice, kill monsters, and get loot. I think it's super fun to play this way.

Dungeons & Dragons touts "The Three Pillars" of progression. Combat, Social, and Exploration. However it seems that most of the Player's Handbook is focused around "how to kill enemies better". For instance, there isn't a "Book of Exploration", but they do have an entire 'Monster Manual". I know, I'm generalizing a lot of the content found in these books, but you get the idea. The Dungeon Master's Guide has some cool chapters on how to do exploration and handle social encounter but definitely not an entire book on these. There are many class features and spells that are not combat focused, but those seem to be mostly perks or afterthoughts.

The players go where the experience is.

I'd like to dive further into the reward system of an RPG and the Three Pillars design in a future post.

_{Quick Side Note: (I think some of my bias might be showing here and I apologize. I love Dungeons & Dragons and it's the system I've play the most in my life. I love it to bits so I don't want it to seem like I'm tearing it down.)}

How does this influence my RPG design? I'm leaning towards horizontal. I'm an open-world, sandbox type of player. Therefore, I'd like to make a system that is open-world and sandboxy. Makes sense, I guess. I understand it's harder to design for, and I have absolutely zero experience designing any system let alone a sandbox. The idea is that players have access to do/gain anything at any time. Hopefully this will allow them to create their own goals as a reward system. We'll see I suppose.

The TL;DR - I want all my game's content to be relevant at any given time. I want the world to feel dangerous (but not oppressive) and the character to forge their own way toward victory. I guess half of this can be designed by the system, and the other half is up the DM anyway, so maybe I'm over thinking it?

Thanks for reading.