Combat

Conditions, New

• Bleeding: A bleeding creature takes the listed amount of necrotic damage at the beginning of its turn, usually one or more exploit dice in the case of Bleed inflicted by a maneuver. Bleeding can be stopped by a using an action to make a Wisdom (Medicine) check at DC 10 + half the die size of the Bleed, or through the application of any effect that allows the creature to regain hit points which rolls an amount of healing equal to or greater than the die size of the Bleed; e.g., DC 18, or a healing spell that rolls 16 or more hit points at once, for a 2d8 bleed effect.
• Dazed: A dazed creature may not take reactions. On its turn, it can either move, or take a bonus action, or take a standard action, but not any two nor three of these.
• Weakened: A weakened creature deals half damage with any attack or effect whose attack roll, damage roll, or save DC is based on Strength, Dexterity or Constitution. For example, a dragon’s breath weapon has a save based on Constitution, so would be affected by the Weakened condition. Spells are not generated from within the body so are exempt from this condition.

Conditions, Revised

• Marked: Marking is a variant rule presented in the Dungeons Masters Guide, and especially relevant to martial characters and many exploits. When a creature marks a target, the mark lasts until the end of the attacker’s next turn unless specified otherwise, and any opportunity attack it makes against the marked target has advantage. The opportunity attack doesn’t expend the attacker’s reaction, but the attacker can’t make the attack if anything, such as the incapacitated condition or the shocking grasp spell, is preventing it from taking reactions. The attacker is limited to one opportunity attack per turn, so you can only react once on a given creature’s turn, but can then react again to a triggering act on another foe’s turn.
• Vulnerable: A vulnerable creature takes additional damage, either of a certain type (e.g., Vulnerable to fire damage) or meeting a certain criteria (e.g., Vulnerable to damage dealt by you). It has a value associated with it, and this is the amount of extra damage that is taken. If no value is given, the default is 50%, rather than the 100% of the book as published.

Critical Hit

• Remember, per 5E Core, any non-static damage modifier that is part of the base attack or phrased as "bonus," "extra," or "additional" is multiplied on a critical hit. On the other hand, static damage modifiers (like from your ability modifier or magic weapon), or a discrete and separate source of damage that simply happens at the same time as the critical (like shoving someone into a trap), are not multiplied.
• The house rule is that critical hits have a minimum damage "floor" equal to the maximum normal damage for that attack.
• For example, if you are rolling 1d8 weapon + 2d6 sneak attack + 4 modifier, and you get a critical hit, you roll double dice and then add modifiers as usual (2d8 + 4d6 + 4), but cannot deal less than 24 damage even if you roll all 1s.

Flanking

• We are using the Flanking “official” optional rule, BUT it is a +2 bonus to hit, not advantage as published.
• This makes it properly the reverse of Cover and allows it to stack with more things.

Natural 20

• A natural 20 on an attack is an automatic hit. If you could have already hit without that automatic hit from the 20, it is also a critical hit. If you would miss the target on a natural 19, that 20 is not a critical!
• A natural 20 on a saving throw is an automatic success. If you could have succeeded without that 20, you may also gain some minor benefit depending on the save. The default is completely avoiding the effect even if it would normally still damage or impact you in some way even on a successful save.
• A natural 20 on a skill check is NOT an automatic success. Some things are just impossible no matter how good you are! But both a success and a failure will be interpreted more generously. It's impossible for you to seduce a dragon, but maybe you amuse them enough that they don't immediately slaughter you for your impertinence.

Natural 1

• A natural 1 on an attack is an automatic miss. If you would have missed already without that 1, that enemy's actions do not provoke opportunity attacks from you until your next turn. There is no other "fumble" effect.
• A natural 1 on a saving throw is an automatic failure. If you would have failed already without that 1, you may also take some additional minor penalty depending on the save. The default is 50% more damage, or disadvantage on your next save for an effect that gives you recurring saving throws to end the effect.
• A natural 1 on a skill check is NOT an automatic failure. Some things your character is just so amazing at they can't fail! But both a success and a failure will be interpreted less favorably. Maybe you don't just fail to climb that wall, but fall partway up and fall on your ass for a die of falling damage.

Non-Lethal Attacks

• More as a reminder than a house rule, there is no special tracking of a separate pool of non-lethal damage in 5E. You just have to declare before you attack that you aren't attacking to kill. You can declare this once for a given enemy instead of having to declare it again with every single attack.
• The optional rule here is that instead of only melee weapon attacks as in 5E core, you can declare any attack to be nonlethal. If it is an area attack, the decision applies to everyone in the area. Flavor it appropriately - maybe your fireball is a blast of kiln-like heat this time instead of flame. I don't care if a "normal" person would have trouble making an attack non-lethal - the kinds of people who go on adventures are not "normal."
• However, at the DM's discretion there are circumstances where your attack or its knock-on consequences logically cannot be declared non-lethal, like when you attack while Confused, your attack causes a cave-in, your spell triggers a wild magic surge (the spell can be non-lethal but the surge may not be), or your attack explicitly causes instant death if it succeeds.

Opportunity Attacks

• Every martial character (someone with at least 1 level of barbarian, fighter, monk, paladin, ranger, or rogue) gets a bonus reaction each round, which can only be used to make one opportunity attack against a creature they threaten who takes a provoking action.
• Casters also get this bonus opportunity attack if they gain proficiency in all martial weapons.
• Enemies also get these opportunity attacks if they are more “martial” than “caster.”
• Characters who gain the Extra Attack class feature gain an additional bonus opportunity attack each round. Those with more than one Extra Attack gain another bonus opportunity attack for each Extra Attack.
• You can only make one attack as part of an opportunity attack, even if you have Extra Attack, unless you are executing an exploit that modifies the opportunity attack.
• No matter how many opportunity attacks you get, any given creature’s turn can only provoke one opportunity attack from you.

Pets

• Animal companions and other "pets" act on your turn.
• A pet can move on its own.
• When you take a bonus action, you can command your pet to take a bonus action if it has one.
• A pet only has one reaction, and does not get a bonus opportunity attack, though you can command it to use its reaction for an opportunity attack.
• By default, your pet can attack once as its standard action.
• If you take the attack action specifically, you can give up one of your attacks to let your pet attack in your stead. In this way, a pet can get two attacks.
• However, you can only benefit from one pet operating independently in this way. If you have two, e.g., an animal companion plus a familiar, you must direct the second one with your own actions as per the usual.

Rounds vs Turns

• Because it's probably the single most common rules confusion point, remember that a "turn" is different from a "round" in the rules. 
• Every character gets a turn every round. A round is thus comprised of many turns. 
• If you have an ability which specifies that it can be used "once per turn" rather than saying "on your turn," you can use that ability even when some rule or interaction allows you to act on someone else's turn. For example, a cleric with Blessed Strike or a rogue with Sneak Attack can use that ability even on an opportunity attack, or when a fighter uses a martial exploit to give them an attack on the fighter's turn, despite having already used the ability on their own turn.

Surprise

• Surprise is probably the single most misunderstood concept in the game, so I am just going to break it down here piece by piece as I under how it works according to Core. There is only a couple house rules here - additional ways to achieve surprise besides just the Stealth skill (literally the only way to do it in Core) and the consequences of being surprised (less severe than in Core). There may be extraordinary circumstances where any or all of the following might logically change, but that can be ruled case by case if it happens.
• 5E does not have a "Surprise Round" per se. Instead, surprise is like a condition, and is determined on a character by character basis rather than for a whole side. One or more characters on any given side of an encounter can be surprised even though their allies are not surprised.
  • You cannot end surprise for someone by shouting a warning or by any other means. The only circumstance in which this works is if you do this before the aggressor initiates the encounter in the first place - before the relevant skill and initiative checks are rolled.
• If you are aware of a creature who is in your presence, they (usually) cannot surprise you, nor vice versa. You usually have to be hidden from someone, and attack them while they are not aware of you, to be able to make them surprised.
  • You can be hidden from someone and they can still be aware of you, such as if you have been taunting them, or you hide during combat. Your target will not be surprised when you attack them in this case. However, you still get advantage on your attack roll against someone who doesn't know where you are, as usual for being hidden.
• If you are in a dangerous place or situation that you already know is dangerous, such as exploring a dungeon, then surprise is usually not relevant. If you come around a corner or open a door and there are creatures there, you are not going to be surprised unless the creatures were actively hidden. By the same token, those creatures will not be surprised by you unless your party was actively stealthy and was actually successful in this attempt, and hasn't already been causing a ruckus within earshot of these creatures such as with an earlier combat.
  • It is almost always passive Insight and passive Perception that apply here, not rolled, save for circumstances like an interrogation for Insight, or active watch or patrol for Perception.
• Spells are always obvious. Their somatic components are dramatic gestures, their verbal components are loud and dramatic, and regardless of components there is always an audiovisual "display" associated with the use of magic. You (usually) cannot surprise someone by casting a spell on them, even if you are hidden.
  • Spells like suggestion are not exempt from this. The verbal component of the spell is separate from and takes place before the effect of the spell. This may not be relevant in normal circumstances if you are using it on someone who is by themselves, or is accompanied by people you are planning to fight anyway, but it is very relevant if you are trying to surprise someone with it or use it in a social situation - everyone will be aware that you are casting a spell!
  • You can achieve surprise with a spell if and only if you have and use the Subtle Spell metamagic, a class feature of the Sorcerer class that you can otherwise only get by taking the Metamagic Adept feat from TCoE.
• If you suddenly declare that you are attacking or casting a spell on someone you are talking to, this (usually) does not surprise them. They can see and hear you just fine. They see you drawing a weapon or starting to cast a spell. Initiative is rolled, and the person you are trying to jump may well go before you do.
  • (House) You can conceal an attack and surprise a target who is already aware of you if you succeed at a Deception or Sleight of Hand check, against the target's Insight or Perception respectively.
  • (House) If the conversation has been relatively hostile, so your intended target is already on edge, this check will take disadvantage.
  • (House) You can conceal a spell and surprise a target if you use Subtle Spell as described above. Even in this event, you must still succeed at a Deception or Sleight of Hand check as noted above.
• You can surprise your own allies, so if you surprise attack like a murder hobo as in the circumstances above where it actually is possible, you are unlikely to be granting any advantage to your allies - unless their passive Perception or Insight detects your intent, your allies will also be debilitated in the first round!
• The action you take to initiate combat when you try to get surprise is your committed action for your first turn. It is not a "free" bonus action, and you can't change your mind about what you're doing! The fact that you might get surprise if successful is in itself the potential reward.
• Even if one or more characters are surprised, the surprised characters still roll initiative with everyone else. This is important, because surprising someone may not be as beneficial as you'd like if they get a higher initiative roll than you.
• (House) The consequences of being surprised are that until the end of your first turn, you have the Dazed condition. As noted in "Conditions," being dazed means that you can't take reactions, and on your turn you can move, or take a bonus action, or take a standard action, but not two or more of these. After the end of your first turn, this goes away and you can take reactions.
• You do not automatically get advantage on attacks against a surprised creature, unless you have a class feature that says so! However, since you usually get surprise by attacking someone while hidden from them, you might still get advantage just from being hidden.

Two-Handed Fighting

• You add your Strength modifier to damage again (minimum +0) when wielding a versatile or two-handed weapon in two hands.
• Even if the weapon has Finesse, this bonus two-handing damage is Strength based!
• You are still treated as having a free hand when using a two-handed weapon, such as to cast spells, since you can just take a hand off your weapon.

Two-Weapon Fighting

• Attacking with two weapons does not take your bonus action.
• When you take the attack action on your turn with one weapon, you can make an additional attack with a weapon in your other hand.
• As per core, unless you have the Dual Wielding fighting style, you only add your ability modifier to the damage of your primary weapon, not to both weapons!