Sort of Thought of Basic 1

Cribbed from Dragonwarriors.
I've just realised that you can use MAGICAL ATTACK as a d20 roll over save or basis for a DC when converting system-to-system. Not perfect, but simple.

Searchers of the Unknown and Lamentations of the Flame Princess are (approximately) the two games I came up with when trying to make D&D-a-like from memory, at the end of my ttrpg hiatus. And then I learned that those two systems already existed (and had for years) when I found out about the OSR.

Basic 1 is a barely-designed Old School adjacent system, nominally based on a version of D&D and a pre-AD&D Gygaxian house-rule. 

It's also a tool for thinking about this kind of game/system - because I'm a tweaker, and the description applies in both senses. Metaphorically.

The system defaults to vanilla fantasy of the kill-the-monsters-claim-the-treasure type, but adapts as well/badly to other genres and styles as any other system. Wherever there are gaps, it's assumed you will either plug in a pre-existing subsystem or make up your own. It's not meant to be D&D, just made out of some of the bits.

This is also how I came to D&D/rpg in the first place - I had some understanding of systems (mainly from gamebooks and reading White Dwarf) and most of the dice, and then the enthusiasm to create, so I tried to make my own before I'd even opened B for BECMI. Pretend you don't own any other dice and just use d6* - this mini-system is also based on me not having a d20 at the same time as not appreciating that OD&D, B/X, BECMI and AD&D were different things.

Because there's nothing new under the sun, I don't know if this already exists - there is only so much information I can reliably process. Comment and links to fait accompli welcomed.

It gets its name from the Epic 6 (E6) hack for D&D 3e, with the alt from the B in BECMI (though could just as well be B/X). Your characters will never rise above 1st level, but they can spend earned XP to boost their abilities for the next adventure. Your enemies will also mainly be 1 (+/-) HD wonders, with the real monsters having 3 or 6 HD.

Characters.

Make four characters, one each of Cleric, Fighter, Magic User and Thief. 

Roll on some random tables to equip and give them backgrounds: your non-class abilities are derived from/implied by these results - characters can do what you expect. You can also use random starting cash to equip them.

This is your stable and can never have more than four characters in it. Preferably, only take one on an adventure at a time, giving the others time to heal, train and/or do research.

Stablemates can share cash and equipment, within reason, but remember to pay for their upkeep while the others are on adventures or they'll starve, fall sick, get kidnapped, be imprisoned for debt or otherwise make real-life trouble for themselves. They can even have jobs, hobbies and off-camera intrigues.

Characters can only be replaced when they die or retire, and retire means you have to set them up for life, not just dump them and take their stuff. Once you are bringing in replacement characters, you are no longer restricted to one of each and you can also start adding non-humans and from other editions/systems.

Hit Dice.

As per BECMI: Fighters d8, Clerics d6, Magic Users and Thieves d4. 

In Basic 1, HD are also used for hitting with.

You can have max. hp, if you want. 

Unless damage is overwhelming, 0 hp or less means you are a Casualty rather than dead - even wounds in combat or having a house fall on you doesn't need to cause hp damage and could have other effects (death save spiral unless rescued, for instance).

Ability Scores.

Classic Six - Strength, Intelligence, Wisdom, Dexterity, Constitution, Charisma - rolled up using whatever method you can all agree on. 

Ability Score Adjustments and Prime Requisites.

Your available/preferred edition of D&D for adjustments and Prime Requisite XP bonus/penalty, or none at all.

Older editions are less generous; AD&D is more detailed/all over the place, and has Percentile Strength for Fighters.

Doing Stuff with Dice and Numbers.

Make rolls (checks, saves, tests, whatever) against Ability Scores using 3d6 roll under (4d6 or even 5d6, if difficult/unskilled/no tools). You can use standard pre-3e and 3e saves, but I've not included them because they were hidden information when I started out.

Using 2d10 or even d20 isn't forbidden. If you want to use d%, the usual thresholds are stat %, x3 and x5. 

Advantage/disadvantage, more-dice-and-drop-some, doubles/triples and crits can all be applied according to situation and taste. Tunnels & Trolls-style saves also valid. If you like, exploding dice can also be a thing.

Thieves can perform all class skills on 1-2 on d6 - but only need to roll in difficult/high pressure situations. The classic Thief skills are class specialisms, and not exclusive - anyone can give them a go, and (say) a Fighter who was a locksmith might be better at lock-picking than an average thief.

Clerics can Turn Undead on 2d6: 7+ for 1- & 1 HD, 9+ for 1+ HD. Clerics Turn 3 and 6 HD undead only on a double six, and are fatigued by success (this is a gap).

Non-Clerics can Turn on double six, but success fatigues. They have no chance to Turn 3 and 6 HD undead.

Combat.

This section is the longest, not because the combat system is the most important part of the game, but because of the legacy of mechanical density and system interpenetration.

The base for the combat system is human vs. human, hand-to-hand - magic, missiles and monsters (including most animals) are all specials. 

Fighting is opposed rolls, HD vs. HD - highest roll wins. Everyone gets to attack and everyone gets to defend. You can use attack vs. defence, or opposed rolls counting for both at once (see Shields below).

Surprise gives you +2 attack/damage and them -2 defence/0 damage. Initiative/First Strike is a gap.

Anything other than melee back and forth (special techniques, tricks, gambits etc) can be resolved with checks/saves/tests, if you don't think the HD is appropriate - this would normally be instead of an attack, but defence may still be allowed.

Gang up to add your HD together for better attack or defence (one wound only if successful, but +1 damage for each ally above 1/you) - you can attack or defend as a group, not both. Logical limits on how many can gang together.

Damage is d6 - Fighters get advantage, Magic Users get disadvantage. Strength adjusts attack/damage. Two-handed weapons get +1 damage. But attacks don't have to cause hit point damage.

You negotiate the difference between weapons through properties and techniques (eg. more people can gang up if using spears; daggers give advantage on attack if you don't defend; tridents can disarm opponents on tied rolls - these are not canon). 

If you really need crits, roll d20 or d% alongside your regular HD for that elusive 5%.

Thieves can use Dexterity bonus to adjust attack/damage. Thief backstab/ sneak attack/ snipe is +4 attack/damage.

If a Fighter kills a +/- 1 HD opponent, they can immediately make another attack (but no defence roll) if there is a suitable enemy within reach. You cannot do 'bag of rats'.

If you are unarmed vs. an armed opponent, you attack with disadvantage. If you are unarmed vs. an armoured opponent, you roll damage with disadvantage.

Shields.

Shields are +1 to your roll, but if you win because of it, you have blocked the attack rather than struck your foe (if it matters, you have still 'won'). Dexterity does the same, though represents dodging and reflexes.

Shields Will Be Splintered applies, but also after each combat roll d4 (cheap/ improvised/ light/ shoddy) or d6 (quality/ heavy shield) - on a 1, the shield is broken and must be replaced. Could also roll vs. 3 HD and 6 HD monster attacks.

Armour.

Leather/chain/plate (or light/medium/heavy) armour as follows (choose/negotiate):

• soaks 1/2/3 damage
• protects completely vs. rolled damage of 1/1-2/1-3
• cumulative protection vs. 1st/2nd/3rd successful hit per combat

After each combat, roll d6 - on a 1, armour degrades one step until repaired or replaced. Roll d4 if vs. a 3 HD monster. Automatic vs. a 6 HD monster.

Magic.

Magic Users get 2 spells - randomly determine or select from appropriate list. You can build up a spell-book and make scrolls. You can purchase more castings as you accumulate treasure and XP (see below).

Check this previous post for some guidance/ideas on using spells from other systems and without levels.

Clerics roll 2d6 to see if they get a spell whenever they start a new adventure (except the first), on a 7+ they have 1. Randomise, select or designate appropriate to deity and faithful behaviour. They can purchase more castings in the same way as a Magic User.

Thieves can use a scroll if they roll double six on 2d6. Or they can buy temporary knowledge of casting (max. 1 or Int mod, whichever is higher) with their treasure/ XP.

Multiple damage dice spells can be divided to reflect individuals affected (as a 'normal' target had a d6 or d8 HD), or the dice can be the saving throw rolled against the relevant Ability Score (ie. a basic fireball rolls 5d6 to beat the target stat to kill/casualty).

Missiles.

If it seems reasonable in a combat encounter, missile weapons can be handled in the same way as melee.

Otherwise, use a Dexterity check/save/test to determine success or failure. 

Thrown weapons, slings and drawn bows can be adjusted for Strength and/or Dexterity to hit and/or damage as appropriate. Being able to use/being equipped with a bow or sling implies a specific skill set for your character.

Crossbows and firearms can be adjusted for Dexterity to hit, but always count as two-handed weapons for damage. Anyone can pick up and use these projectile weapons (for the purposes of Basic 1).

Monsters.

Most common monsters will have +/- 1 HD. The exact die used can be based on the edition (d6, d8, 3e+ monster type HD etc). This covers anything with +/- HD or less in D&D adjacent material, and is the default for anything approximately humanoid and adult human-sized.

3 HD monsters are the Bears and Ogres and Trolls; 6 HD are the Dragons and Elephants and Giants.

3-6 HD monsters roll all their HD to attack and defend, representing how hard it is for normal humans to just go toe-to-toe with them. They can also have an attack allowing them to use all their HD as damage dice or split between multiple targets. Your mission is always to find a better way so that you don't have to go dice-to-dice - at the very least, you need to gang up and/or grapple/overbear them. 

Use raw numbers from printed HD to give + to hp and combat rolls where a Basic 1 1 HD monster falls into the grey area (ie. Bugbear can be 1 HD +4 hp & combat rolls). 

Give monsters special abilities to reflect why they have high HD RAW when converting - sometimes the answers will already be in the description. Damage caused is less important than the mechanical/ narrative effects (eg. your equipment being set alight is more important/interesting than what dice is rolled for damage RAW).

Monsters have default Ability Scores of 9 + HD for special cases and saves, adjusted as seems appropriate and/or based on their description. Ability Scores don't mean the same for monsters as they do for characters.

Monsters do not have to stick to the same rules as the players, but not as an excuse for unfunny TPKs.

Experience and Treasure.

Lots of gaps here.

You purchase benefits for the next adventure using XP and/or treasure. I'm being deliberately vague on what benefits are, because you might be able to bring something to the narrative/world-building with it - like you purchase an ally who will turn up when needed, a weather event that suits your plans, even a safe place to rest in the dungeon.

Treasure can be spent on any character in the stable, but XP is specific to the character that earned it.

If you aren't planning to use an existing subsystem, awards and costs could be drawn from a pre-existing, repurposed chart:

Search for 'xp budget' or 'xp threshold' to find more charts - other editions, other games, bloggers etc.
Another good one here.

Want to know how much XP surviving the 5th level of the Deadly Dungeon? It's right there.

Want to buy an ability or a spell tied to a high level? Look it up and start negotiating.

I'd make costs cumulative and maybe apply a hard cap of 5 benefits max. or 1 benefit + 1 per previous adventure for each character, but you don't have to.

Buying an ability outside your class will always be more expensive, but I don't see why you shouldn't do so. If you've got access to the material, you can buy Feats if you can make them run within Basic 1; the same with magic items - though they're only good for the next adventure (give them a usage/refresh die rather than charges, and you can buy the same one next adventure and say it's still the original one).

Ability Score advances would be priced according to the relation to your class and the levels they would normally apply (generally every four levels) - cumulative costs, so three advances would be (using the Easy column above) would be 125+450+1,000=1,575 rather than 375.

An alternative is to use something like Spwack's X System for DIE TRYING, which I first encountered in Sofinho's PARIAH.

*If you've only got d6, Fighter HD becomes d6+1 and everyone else d6. The d4 roll for shields vs. 3 HD monsters can become a d6-1 or d3 roll.

Commentary.

I needed a break from thinking and writing about Monster Manual 2, and this is the result - clearing out some of those crowding background thoughts and giving me something to refer back to.

I'm also getting some emerging combat/encounter system ideas in opposition to the rather one-size-fits-all approach of D&D.

It's probably a broken system, but it's more for thinking with than playing with. 

The primary driver behind pulling this thing together was reading this post at Dreaming Dragonslayer about Rogue Runs in Darkest Dungeon (which I've been enjoying as a play-style) and this post at Wodan Gaming about doing away with spell levels (and the linked Zzarchov Kowlaski post).