An individual player can control up to two creatures at a time while in combat. This limitation includes, player characters, familiars, animal companions, mounts, summoned creatures, and sidekicks. This limitation does not apply to creatures aiding you outside of combat, such as retainers or beasts of burden.
At any time, you may bestow control of a creature to another player that is not already controlling two creatures.
A long rest may only be completed in a Haven, such as a warm inn, a fortified keep, or a magical sanctum.
Flanked. A flanked target has a -2 penalty to AC and Dexterity saving throws. A creature is flanked if there are creatures or obstacles covering two opposing sides of it.
Surrounded. A surrounded target has a -5 penalty to AC and Dexterity saving throws. A creature is surrounded if there are creatures or obstacles covering all sides of it.
The Two-Weapon Fighting style reads as: "When you engage in two-weapon fighting, you can add your ability modifier to the damage of the second attack, which doesn't require your bonus action."
Each time you level up, you roll all of your hit dice, adding your constitution modifier, and use the total as your new hit point maximum.
If circumstances cause a roll to have both advantage and disadvantage, you are considered to have both of them, and you roll three d20s, using the middle roll.
Each character has supplies, which represents their ability to plan for what they might need on your adventures. You use supplies to replenish spent equipment, like ammunition, food and water, or tool parts. You can gain supplies by foraging, hunting, or simply purchasing some at the convenience of a settlement or traveling merchant.
Supplies only refuel the equipment you already had—supplies can't be used to spontaneously create "quantum equipment".
Items and weight are tracked in terms of load. Each item (or bundle of similar items) is generally 1 load. You can carry load equal to your Strength score without issue.
Light armor is considered to be 1 load, medium armor is considered to be 2 load, and heavy armor is considered to be 3 load. A weapon with the Heavy property is considered 2 load, and a pair of weapons with the Light property makes up 1 load.
If you are encumbered, your speed is reduced by 5 feet for every point of load over your Strength score, you can only travel at a slow pace (but do not gain the benefits of doing so), and you have disadvantage on any ability check, saving throw, or attack roll that uses Strength or Dexterity.
If you spend 1 minute carefully drinking a potion of healing, you regain the maximum amount of health it can restore.
If you spontaneously establish a connection between your character and a proper noun in the game world, the DM may award you with Inspiration. If the relationship is antagonistic or otherwise problematic, the DM may also award you with Inspiration that you can grant to a party member of your choice.