D&D 5e Brutal Low-Fantasy Hack

The purpose of this hack is to take the 5e system and gut the things that make it heroic high fantasy.  It removes the need to concern yourself with complex character creation that is aimed at optimizing a character.  It uses the oracular approach to character creation.  With this hack, all the players need to do is get a copy of the free Basic 5e rules.  There's absolutely no need to give WotC hundreds of dollars to keep up with the latest additions to the system.

Here are the pros:

• All adventurers share a common history/background. They've seen some shit. They're part of the world. They're capable but not too capable. Magic is less predictable, more risk/reward.
• Adventurers end up having a little extra HP at first level but there isn't the problem of HP bloat of higher levels
• Spells don't get too ridiculous. Creatures and deities will be sought to deal with conditions that level4+ spells might make a non-issue (namely death and dismemberment).
• Preserves class niche to a better extent due to the limiting of certain higher level class features and multiclass combinations.
• Replacing proficiency bonus with character level means every level, your skills improve substantially. Even more so with expertise

Here are the cons:

• Players won't have their finely tuned character concept realized.  Rather, they'll have to learn how to turn a rock into a diamond.  Not mechanically, but thematically.
• PCs will die.  They will probably die often.  This can get frustrating, but this gives survival a feeling of accomplishment that is often missing without prolonged slugging matches in standard 5e. Also, this is why character creation is simplified.
• PCs will never be "Gods Among Mortals."  The level cap is at 6, which is substantially stronger than your average commoner, but they can always mob you and stab you to death.  This is meant to be more grounded than heroic fantasy.
• This requires more creativity on the DM's part to "wing it" when certain things happen.  Because of this, the players will need to have a level of trust with their DM, that they're not out to destroy them, but give them an immersive experience with significant consequences, risks, and rewards.

PC RULE CHANGES:

Rule Zero: What the DM says still goes.  This isn't a change, it just should be reiterated.

1. Utilize Dungeon Crawl Classics' character funnel approach. (preferred, but optional).  If you do not use this, skip to #2.

-Players start with several PCs each (3 or 4), all classless at level0, with just a d4+CON.

Roll a random table for an occupation (either make the table yourself appropriate to your setting, or use a pre-existing one, they're easy to find) and approximate starting gear. No death saves til level1.  You hit zero, you die. You run through an adventure with these characters and the survivors get to become level1 adventurers.  Some game-time should pass while they develop their craft.

2. A level 1 adventurer will gain their class features along with that full Hit Die of HP (ex the Fighter will get an additional 10 HP on top of the level0 d4+CON hp). PC levels cap at level6. No multiclassing. No feats. Basic Rules races, spells, classes, & subclasses only (Basic Rules subclasses: Champion for Fighter, Life for Cleric, Evocation for Wizard, Thief for Rogue).  "Backgrounds" as written in 5e do not exist and are replaced with Occupations as mentioned in #1.

3. On a level up, characters get their features as normally, except for the following changes:  On every level increase, you can add +1 to any ability score two times, meaning by level 6 you will have an additional +12 points in your ability scores (since this includes the ability score increase at level4). Instead of getting a hit die+CON added to your maximum HP for every level up, you get your full hit die divided by two. Fighters, for instance, get 5 HP. This is unadjusted by CON.

4. SPELLCASTING:  There are NO SPELL SLOTS.  Casting ANY spell requires spellcasting rolls using d20+spellcasting modifier + character level (this would cap at +9). To successfully cast the spell, the player must roll a DC of 6+(spell level*2).  Example: A cantrip requires a casting DC of 6.  A level 1 spell requires a casting DC of 8.  A level 2 spell requires a 10. A level 3 spell requires a 12.  Simply failing to cast your spell means you cannot try to cast this spell again until after a Long Rest.
Nat 1 = mishap.  If a mishap occurs, roll again to see how severe it is and approximate the effect.  If it's another Nat 1, it should be catastrophic.  If it's a Nat 20, it shouldn't be that bad at all.
Nat 20 = The spell is extremely potent.  Add more duration, more damage, more effects, whatever.  Make it cool.

5. Proficiency bonus is replaced by character level in all calculations (save DCs, expertise, etc).  Yes, ALL CALCULATIONS!  This means when you make an attack roll with a finesse weapon, you Roll d20+character level+DEX or STR.  If you make a skill roll and you have expertise, you double your character level in the calculation.

On the DM side:

Rule Zero: Don't be a dick to your players.

1. Players no longer get their entire pool of HP back on a long rest.  They still get 1/2 (rounding up) their pool of hit dice back on a long rest.  This means that if they're completely exhausted, they may need to rest two days just to be fully healed.  They may want to rest two more to refill their hit dice to the max.  This promotes downtime.

2. Downtime is encouraged to be used to build connections with NPCs, grow a stake in the game world, hire people for assistance, perform quests that do not require combat, and take time to learn a new skill to be proficient in.  This encourages narrative-driven character growth of skills.  

3. Monster HP should be scaled down to half since PCs will be capped at level6 and with less HP than normal.

4. Let players be creative.  Though there are no feats, PCs should be able to try things that are approximate to feats.  An example would be attacking a specific body-part.  They should be able to attempt this with a -5 penalty on their to-hit roll.

5. Darkvision does not exist for PCs at all.  This encourages risk vs reward.  Dark places are meant to be dangerous and a lighting source can help them stay safe, but it makes them more noticeable.  

6.  Be fair, be consistent, but be confident in your ability to approximate things.  

7. Some skills cannot be attempted without proficiency in them. Use your best judgment. My suggestions are that this would include: Knowledge Rolls such as Arcane, History, Religion, and Nature as well as Technical Rolls such as Survival and Animal Handling.  Medicine would be a combination of these two.  For the rest of the skills, they can be attempted, but if someone is proficient in these skills, they may not need a roll to tell whether or not they succeed.

8. Be flexible when it comes to flavoring and descriptions.  Let the players be creative.  If they want to describe their abilities in a certain way that doesn't openly defy the spirit of your game, let them.  If they want to trade a class feature for another class feature and this class feature doesn't defy your game world's parameters, let it happen.  Example: Let a fighter replace Fighting Style with Martial Arts, Action Surge with Unarmored Defense, etc.  The important thing is that the Fighter is still fulfilling the Fighter's role in every way that matters.

9. Use random tables for injuries (which happens when a PC hits 0 HP), fumbles, and critical effects.  Get them wherever you'd like.  These can be found in the DMG and in Critical Hit / Fumble Decks or just on forums.

When I talk about looking to tables for additional support, here are some of the things I'd use: Occupations: DCC's Beta Rules (Or just buy the full game. It's brilliant and you won't regret it). Goodman Games has the PDF here: http://goodman-games.com/downloads/DCCRPGBeta060811.pdf… (p15)
Injuries (@ 0hp): http://farlandworld.com/injuries.html The Critical Hit / Fumble charts on the DCC Rules are also fantastic. Or, you can always approximate it based on the situation. Just keep in mind that you need to be reasonable and not shoot for a certain outcome.