Rules

Climb onto a bigger creatures: Rules to allow a small or medium character to climb onto a “suitably large” opponent. A contested Athletics/Acrobatics roll vs. Acrobatics is all that is required for the smaller character to climb onto the larger one and start clambering around him as if the larger creature is difficult terrain. This seems flavourful and is easy to adjudicate. The smaller creature moves with the target and has advantage on attack rolls. If the larger creature hits the smaller creature they need to make an Athletics/Acrobatics check to stay on the creature. The larger creature can try to get the smaller creature off at the end of each of its turns
Overrun: This option is used when you want to push through a hostile creature’s space. It’s a simple contested Athletics check – the larger character getting advantage on the check. If you succeed you can travel through the creatures space.
Shove aside: The ability to shove a creature backwards (and perhaps push them over) is part of the core rules and listed by p195 of the PHB.
Shoving a Creature Using the Attack action, you can make a Special melee Attack to shove a creature, either to knock it prone or push it away from you. If you’re able to make multiple attacks with the Attack action, this Attack replaces one of them. The target must be no more than one size larger than you and must be within your reach. Instead of Making an Attack roll, you make a Strength (Athletics) check contested by the target’s Strength (Athletics) or Dexterity (Acrobatics) check (the target chooses the ability to use). If you win the contest, you either knock the target prone or push it 5 feet away from you.
Tumble: This allows a character to make an opposed Acrobatics check to move through an opponent’s space similar to overrun.
Dash When you take the Dash action, you gain extra Movement for the current turn. The increase equals your speed, after applying any modifiers. With a speed of 30 feet, for example, you can move up to 60 feet on Your Turn if you dash. Any increase or decrease to your speed changes this additional Movement by the same amount. If your speed of 30 feet is reduced to 15 feet, for instance, you can move up to 30 feet this turn if you dash.
Disengage If you take the Disengage action, your Movement doesn’t provoke Opportunity Attacks for the rest of the turn.
Dodge When you take the Dodge action, you focus entirely on avoiding attacks. Until the start of your next turn, any Attack roll made against you has disadvantage if you can see the attacker, and you make Dexterity Saving Throws with advantage. You lose this benefit if you are Incapacitated (as explained in Conditions ) or if your speed drops to 0.
Help You can lend your aid to another creature in the completion of a task. When you take the Help action, the creature you aid gains advantage on the next ability check it makes to perform the task you are helping with, provided that it makes the check before the start of your next turn.
Alternatively, you can aid a friendly creature in attacking a creature within 5 feet of you. You feint, distract the target, or in some other way team up to make your ally’s Attack more effective. If your ally attacks the target before your next turn, the first Attack roll is made with advantage.
Hide When you take the Hide action, you make a Dexterity (Stealth) check in an attempt to hide, following the rules for Hiding. If you succeed, you gain certain benefits, as described in the “Unseen Attackers and Targets” section.
Ready Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on Your Turn, which lets you act using your Reaction before the start of your next turn. First, you decide what perceivable circumstance will trigger your Reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. Examples include “If the Cultist steps on the trapdoor, I’ll pull the lever that opens it,” and “If the Goblin steps next to me, I move away.”
When the trigger occurs, you can either take your Reaction right after the trigger finishes or ignore the trigger. Remember that you can take only one Reaction per round.
When you ready a spell, you cast it as normal but hold its energy, which you release with your Reaction when the trigger occurs. To be readied, a spell must have a Casting Time of 1 action, and holding onto the spell’s magic requires Concentration. If your Concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready Magic Missile, your web spell ends, and if you take damage before you release Magic Missile with your Reaction, your Concentration might be broken.
Search When you take the Search action, you devote your attention to finding something. Depending on the Nature of your Search, the GM might have you make a Wisdom (Perception) check or an Intelligence (Investigation) check.

Use an Object You normally interact with an object while doing something else, such as when you draw a sword as part of an Attack. When an object requires your action for its use, you take the Use an Object action. This action is also useful when you want to interact with more than one object on Your Turn.
Grappling When you want to grab a creature or wrestle with it, you can use the Attack action to make a Special melee Attack, a grapple. If you’re able to make multiple attacks with the Attack action, this Attack replaces one of them.
The target of your grapple must be no more than one size larger than you and must be within your reach. Using at least one free hand, you try to seize the target by making a grapple check instead of an Attack roll: a Strength (Athletics) check contested by the target’s Strength (Athletics) or Dexterity (Acrobatics) check (the target chooses the ability to use). If you succeed, you subject the target to the Grappled condition (see Conditions ). The condition specifies the things that end it, and you can release the target whenever you like (no action required).
Escaping a Grapple: A Grappled creature can use its action to escape. To do so, it must succeed on a Strength (Athletics) or Dexterity (Acrobatics) check contested by your Strength (Athletics) check. Moving a Grappled Creature: When you move, you can drag or carry the Grappled creature with you, but your speed is halved, unless the creature is two or more sizes smaller than you.
Cover Walls, trees, creatures, and other obstacles can provide cover during combat, making a target more difficult to harm. A target can benefit from cover only when an Attack or other effect originates on the opposite side of the cover. There are three degrees of cover. If a target is behind multiple sources of cover, only the most protective degree of cover applies; the degrees aren’t added together. For example, if a target is behind a creature that gives half cover and a tree trunk that gives three--quarters cover, the target has three--quarters cover. A target with half cover has a +2 bonus to AC and Dexterity Saving Throws. A target has half cover if an obstacle blocks at least half of its body. The obstacle might be a low wall, a large piece of furniture, a narrow tree trunk, or a creature, whether that creature is an enemy or a friend.
A target with three--quarters cover has a +5 bonus to AC and Dexterity Saving Throws. A target has three--quarters cover if about three--quarters of it is covered by an obstacle. The obstacle might be a portcullis, an arrow slit, or a thick tree trunk.
A target with total cover can’t be targeted directly by an Attack or a spell, although some Spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.
Instant Death Massive damage can kill you instantly. When damage reduces you to 0 Hit Points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum.
For example, a Cleric with a maximum of 12 Hit Points currently has 6 Hit Points. If she takes 18 damage from an Attack, she is reduced to 0 Hit Points, but 12 damage remains. Because the remaining damage equals her hit point maximum, the Cleric dies.
Knocking a Creature Out Sometimes an attacker wants to incapacitate a foe, rather than deal a killing blow. When an attacker reduces a creature to 0 Hit Points with a melee Attack, the attacker can knock the creature out. The attacker can make this choice the instant the damage is dealt. The creature falls Unconscious and is stable.
Mounted Combat A Knight charging into battle on a Warhorse, a Wizard casting Spells from the back of a Griffon, or a Cleric soaring through the sky on a Pegasus all enjoy the benefits of speed and mobility that a mount can provide.
A willing creature that is at least one size larger than you and that has an appropriate anatomy can serve as a mount, using the following rules.
Mounting and Dismounting Once during your move, you can mount a creature that is within 5 feet of you or dismount. Doing so costs an amount of Movement equal to half your speed. For example, if your speed is 30 feet, you must spend 15 feet of Movement to mount a horse. Therefore, you can’t mount it if you don’t have 15 feet of Movement left or if your speed is 0.
If an effect moves your mount against its will while you’re on it, you must succeed on a DC 10 Dexterity saving throw or fall off the mount, landing prone in a space within 5 feet of it. If you’re knocked prone while mounted, you must make the same saving throw.
If your mount is knocked prone, you can use your Reaction to dismount it as it falls and land on your feet. Otherwise, you are dismounted and fall prone in a space within 5 feet it.
Controlling a Mount While you’re mounted, you have two options. You can either control the mount or allow it to act independently. Intelligent creatures, such as Dragons, act independently.
You can control a mount only if it has been trained to accept a rider. Domesticated horses, donkeys, and similar creatures are assumed to have such Training. The Initiative of a controlled mount changes to match yours when you mount it. It moves as you direct it, and it has only three action options: Dash, Disengage, and Dodge. A controlled mount can move and act even on the turn that you mount it.
An independent mount retains its place in the Initiative order. Bearing a rider puts no restrictions on the Actions the mount can take, and it moves and acts as it wishes. It might flee from combat, rush to Attack and devour a badly injured foe, or otherwise act against your wishes.
In either case, if the mount provokes an opportunity Attack while you’re on it, the attacker can target you or the mount.
Underwater Combat When adventurers pursue Sahuagin back to their undersea homes, fight off sharks in an ancient shipwreck, or find themselves in a flooded dungeon room, they must fight in a challenging Environment. Underwater the following rules apply.
When making a melee weapon Attack, a creature that doesn’t have a swimming speed (either natural or granted by magic) has disadvantage on the Attack roll unless the weapon is a Dagger, Javelin, Shortsword, spear, or Trident.
A ranged weapon Attack automatically misses a target beyond the weapon’s normal range. Even against a target within normal range, the Attack roll has disadvantage unless the weapon is a crossbow, a net, or a weapon that is Thrown like a Javelin (including a spear, Trident, or dart).
Creatures and Objects that are fully immersed in water have Resistance to fire damage.
Crafting a Magic Item (DMG p128) Rules in an expanded section
Equipment Sizes (PHB p145) A common sense optional rule that basically says that armour and clothing that fits one character won’t necessarily fit someone else. Yes, I can’t believe this is a variant rule rather than a default assumption, but there you go. What this means in practice is that if you kill a 7’5″ bugbear and steal his full plate armour, you’re going to need to employ a smith to do some considerable work resizing it for your dwarven paladin.
Feats (PHB p165) Yes, we are going to be using the optional feat rules. No discussion here, I think that they really help to flesh out your character. Any time you would gain an ability score increase during leveling you can choose to take a feat instead.
Using the environment and create solutions Don't be afraid to get creative. I care much more about story and narrative then I do about mechanics. (I also have an entire set of tables dedicated to improvised damage and effects). If you want to do something or try something than go for it. Let me know what you want to try, I'll give you the necessary warnings and obstacles, and then go for gold. I'll always try to balance the actions and consequences so that the mechanics don't break and the game has weight to it but I don't want you to feel shackled by the mechanics.
More Difficult Magic Item identification (DMG p136) Under the normal rules you can identify any magic item by handling it and experimenting with it over the course of a short rest. By the end of the short rest, you know all these is to know about the item. I think that’s a bit dull. Magic items are, after all, supposed to be unique items of power in 5th edition. Therefore you’ll need to cast the Identify spell, or embark on some serious empirical research, to learn all there is to learn about a magic item. Some may give up their secrets easily, others may not.
Multiclassing (PHB p163) D&D would not be D&D without multiclassing, and I wouldn’t dream of removing this option from the game. However, consider the ramifications before you multiclass as it’s easy to create a mechanically sub-optimal character through multiclassing, and the concept you’re going for might be better reflected with a background or feat. I’m not against multiclassing within the same class to gain the benefits of two different archetypes in principle, as long as the resulting character isn’t an obvious nonsense. However, I think that in practice the resulting character would be pretty weak compared to his companions. We’d have to look at this on a case-by-case basis. So, Multiclassing is an option, but it’s very much buyer-beware.
Sanity and Madness Some things are so traumatic that they can cause the characters to go mad or lose sanity. While I don't plan on using this throughout the whole campaign there may be certain times when the stability of your minds are tested. Like injuries I think these can get fairly crippling fairly quickly but the lighter variants I think add flavor and interest to things. Consequences. There are also spells that inflict madness on creatures and magics meant to cure said madness which can be fun to play with.
Scrolls To use a scroll is an action. If it is a spell on your spell list you use the scroll no problem. If it is not on your spell list then you need to make an Arcana check at 10+the spell level. If you succeed then the spell activates. If you fail then roll a d12. If you roll the spell level or lower then the scroll has a magic mishap.
Skills with Different Abilities As I mentioned in the previous post on skills, one of the variant rules allows the player or the DM to suggest using a different ability score when making a proficiency check. For example, swimming is normally a Strength (Athletics) check, but if you’re trying to swim a very long distance the DM might decide that success is more dependent on your endurance than brute force. He might therefore call for a Constitution (Athletics) check instead. It’s a rule to be used sparingly, and players are encouraged to suggest creative uses of their abilities in particular circumstances.
Downtime Downtime is time we don't spend playing. So the characters are doing things, we have a montage, whatever. These are times usually when your characters are training, doing maintenance things, or just relaxing. There's a whole section for this including crafting items and spells, buying and selling goods, sowing rumors, starting businesses, training in languages, skills, or other proficiencies, sometimes even gaining levels or new abilities that they learn from teachers.
I like downtime. Inventory and Money Your inventory and money management are yours to deal with. You are in charge of what you have and what you don't. Also I plan on money having a bit more weight in this as well so don't expect to be drowning in gold coins every time you do something. I think that having limitations makes the game more fun in ways.
Lifestyle Expenses Lifestyle Price/Day Wretched —- Squalid 1 sp Poor 2 sp Modest 1 gp Comfortable 2 gp Wealthy 4 gp Aristocratic 10 gp minimum Services Service Pay Coach cab Between towns 3 cp per mile Within a city 1 cp Hireling Skilled 2 gp per day Untrained 2 sp per day Messenger 2 cp per mile Road or gate toll 1 cp Ship’s passage 1 sp per mile
Falling A fall from a great height is one of the m ost com m on hazards facing an adventurer. At the end of a fall, a creature takes 1d6 bludgeoning damage for every 10 feet it fell, to a maximum of 20d6. The creature lands prone, unless it avoids taking damage from the fall.
Suffocating A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds). W hen a creature runs out of breath, it can survive for a number o f rounds equal to its Constitution modifier (minimum 1 round). At the start of its next turn, it drops to 0 hit points and is dying.
Luck points Instead of inspiration you can accrue luck points. You can use luck points to do the following. Spend 1 luck point to roll a d4 to add or subtract to a roll of your own Spend 2 luck points to roll a d4 to add or subtract to a roll of someone elses
Secret death checks I will roll your death checks so no one will know how you're doing
Smarty Pants Based on your Intelligence modifier you add to or subtract from proficiencies you have. If your intelligence raises during leveling then you can choose a new proficiency.