D&D 5e House Rules

When my first D&D 5e campaign kicked off in 2015, I committed myself to running the rules as written (RAW) because I intended to publish content I developed over my four decades of playing and running the game. I wanted to ensure that I understood the game as intended and that any house rules or incorrect interpretations didn't bleed their way into my material. I also wanted my players to be confident that what they read in the PHB was what they experienced over Roll20.

This worked well except, over time, I grew increasingly dissatisfied with the game's default "easy" mode. So many elements are rendered trivial by the designers' desire to make the game "safe" and survivable, that much of the risk (and fun) is removed. That might be fine for brand-new players, but my veteran players were used to the difficulties of earlier editions, and became frustrated when they would, for instance, finally land a spell effect on the BBEG, only to have the target shrug off the effect on its next turn.

Now that we all have a few years under our belts and know the RAW version, I've begun incorporating a few house rules to address some of the things I don't like.

ARMOR

• Medium armor = 5 ft. penalty to Speed; disadvantage on Stealth checks.
• Heavy armor = 10 ft. penalty to Speed; disadvantage on Perception and Stealth checks.

DARKVISION
The ability to see in darkness is now divided into two separate traits: night vision, which allows a creature to see outside, under the ambient light of the moon and stars; and dark vision, which allows a creature to sense heat variations underground.

• Above-ground creatures with the darkvision trait (most beasts, elves, half-orcs, etc.) have night vision instead.
• Subterranean creatures (dwarves, goblins, etc.) have dark vision.
• Some creatures (like undead and dragons) have both.
• The 2nd-level darkvision spell confers both types upon the recipient as well.

In BOTH cases, creatures see in dim light as though it was bright light, and in total darkness as though it was dim light. Creatures are blind beyond the maximum range of their enhanced vision (as a human is in darkness).

DYNAMIC COMBAT
A creature can attack through an ally's space at disadvantage, even if they are behind the ally. Doing so means the creature can also be targeted by the front rank of the opposing side on the opponent's turn, even if they are not in direct engagement. This tactic is especially useful when fighting in narrow passages or through doorways. 

LOOTING CORPSES

• It takes (3) rounds to search a body for loot.
• It takes (10) minutes to extract essences from a slain creature.

PICKING LOCKS / DISARMING TRAPS
Attempting either of these activities requires proficiency with thieves tools and (1) round times (DC / 5) .

• Anyone using their action to Help the attempt must also be proficient in thieves tools. 
• Failing a pick lock check allows follow-up attempts, requiring another time period and increasing DC by 2 each time. After (3) failed attempts, the lock is beyond the character's ability to pick until their Proficiency bonus increases.
  
• Failing a disarm traps check automatically springs the trap.
  

RANGED ATTACKS INTO ENGAGEMENT
Making a ranged weapon or spell attack against a target who is engaged in combat with at least one opponent within 5 ft. of it is considered to have 3/4 cover (+5 AC) regardless of the attacker's line-of-sight.

• If the ranged attack misses the intended target, the attacker must make another attack against one random creature within 5 ft. of the original target. (The target of this attack also has 3/4 cover for being engaged.) 
• If the second attack misses, the ranged attack misses all combatants. If it hits, roll normal damage against the new target.

SAVING THROWS VS. EFFECTS 

1) Ongoing Effects. When a creature fails the initial saving throw to resist a harmful effect and then suffers an ongoing duration of effect (such as charm, fear, or poison), any follow-up saves made at the end of their turn to end the effect have disadvantage.

2) Effect Immunity. Some creatures have abilities that require the target(s) to make a saving throw to resist, which, if successful, renders the target "immune to the [EFFECT] for the next 24 hours." (EX: a dragon's Frightful Presence effect).

Unless otherwise noted, a target creature is never made immune to an effect by virtue of having made a successful saving throw to resist it. Instead, if the character makes the initial save, all subsequent saves against the same effect are made at advantage.