Play your Roll
A "Natural 20" happens when the natural result of the used d20 in a "d20 Test" is the maximum value, 20. It allows the player to instantly succeed at the attack roll, saving throw, or ability check it concerns, with additional benefits, including doubling an attack's amount of damage dice, or completely avoiding damage from a saving throw when a creature normally would take half.
"Natural 20"s do not guarantee success nor give any additional effects in saving throws or ability checks.
Certain weapons have special properties, which govern how they act. "Heavy" weapons give disadvantage on attack rolls to Small or smaller creatures who use it, "Finesse" weapons use Dexterity to calculate the attack and damage rolls instead of Strength, and "Reach" weapons allow the wielder to make melee attacks from 5 extra feet away.
Finesse weapons give the choice of using Dexterity or Strength
If a creature falls from a great height, they immediately descend 500ft, or until they collide with the ground. At the end of each of their turns, if they are still falling, they repeat the 500 foot movement again. Once the creature hits the ground, they take an amount of d6s in bludgeoning damage equal to 1/10 of the distance the creature fell.
Falling damage caps at 20d6.
Monsters are measured by Challenge Rating (CR), which denote their approximate difficulty in battle. The highest CR a creature could have is CR 30; the only two creatures who are CR 30 are the Tarrasque and Tiamat.
CR can go higher than 30
The Ability modifiers of your stats are almost always used instead of the actual Ability Score; it is still used in some niche cases, though. Some examples include the following: When jumping across a large gap, you can safely long jump a number of feet equal to your Strength Score without a check, if you get a running start. A Medium creature can carry a maximum of 15 times its Strength Score in pounds. For each size above Medium, double that amount, and for each size below, halve that amount.
Only for each size below Small does the maximum carry capacity halve
Armor may be worn to alter a creature's AC. The amount of AC varies with Dexterity for Light and Medium armor, while Heavy armor is unaffected by Dexterity. To compensate for this benefit, most Heavy Armor requires a certain amount of Strength to be donned, and provides Disadvantage on Stealth checks while worn.
Not meeting a Heavy Armor's Strength requirement only reduces your speed by 10ft, not prevents you from wearing it
There are various spells currently are or were once named after the magic-wielders who created them. Such spells include Tasha's Hideous Laughter, Noanar's Fireball, Otiluke's Resilient Ball, and Tenser's Floating Disk.
It's Otiluke's Resilient Sphere, not Ball
If a Druid Wild Shapes into an animal with a Special Sense, they gain that special sense. For example, a Human Druid would gain 60ft Darkvision while they are Wild Shaped into a Cat. Alternately, if a Druid who already has a special sense transforms into an animal without it, they lose that sense. For example, if a Tiefling Druid Wild Shapes into a Horse, they no longer have Darkvision.
Cats do not have darkvision
Full casters in D&D are reliant on various mental-related ability scores to increase the power of their spells. Clerics are reliant on Wisdom, Sorcerers rely on Charisma, and Artificers Intelligence.
Artificers are not Full Casters.
Gold Pieces (GP) are the standard unit of value in the DnD world. In addition to GP, there also exists the Silver Piece (SP), Copper Piece (CP), Electrum Piece (EP), and Platinum Piece (PP). Each coin weighs about a third of an ounce, no matter the denomination. A CP is 1/100 of a GP, SP 1/10, EP 1/5, and PP are 10x as valuable.
Electrum Pieces are worth 1/2 a GP.
The "Ring of Resistance" is a magic item which, while attuned, provides Resistance to a damage type to the wearer indicated by the type of gem set in it. "Resistance" reduces the incoming damage to a creature to half of the damage, rounded down. If a creature were to attune to three Rings of Resistance all of the same type, they would still take only half damage from that type of damage, because the resistance does not stack.
A creature cannot attune to more than one copy of the same magic item, so this can't happen.
Many spells summon beasts, like Find Familiar, Conjure Animals, and Summon Beast. Find Familiar summons a beast from a premade list of beasts, Conjure Animals summons 2 CR worth of any amount of beasts, and Summon Beast allows a choice between a Land, Air, and Sea beast, with the same stat block for every animal in each type for easier use.
None of these spells actually summon beasts; they all spell fey spirits that take the form of a beast.