Yes, those're the rules.
That's really all there is to it. Except here's a bit more.
PS: I know D&D isn't meant to be a realistic sumulation, but still.
There are times in the history of D&D when it's tried to be a more-realistic simulation. For your purpose I'd recommend taking a look at racial bonuses/decrements to stats; perhaps the PHB1e?
Yes, the creature is dead when it reaches 0 hit points.
Basic Rules (p. 79)
When you drop to 0 hit points, you either die outright or fall unconscious...
This can be modified for a monster, but usually 0 HP = dead monster:
Basic Rules, (p. 79)
Most DM's have a monster die the instant it is dropped to 0 hit points, rather than having it fall ...
Magic is unaffected by creature size. Creatures can have benefits for particular types of magic (it’s easy to imagine a dragon getting bonuses on fireball—after all, their descendants do—or a pixie getting some benefit with illusions), but nothing automatic just for being larger. Any such benefit would be listed directly in the creature entry.
In this context "Large" means of the Large size category (Player's Handbook p.191), meaning it occupies a 10' by 10' space. The exact phrase is the following:
The yuan-ti can use its action to polymorph into a Large snake, or back into its true form.
Note that the capital-L Large refers to a size category, not a general indication of bigness.
There's a factor you missed out on: the square-cube law. As Wikipedia describes it:
When an object undergoes a proportional increase in size, its new surface area is proportional to the square of the multiplier and its new volume is proportional to the cube of the multiplier.
Let's consider the implications of this for a moment with a cube of water: it ...
The rules read
When an article of magic clothing or jewelry is discovered, most of the time size shouldn’t be an issue. Many magic garments are made to be easily adjustable, or they adjust themselves magically to the wearer. Size should not keep characters of various kinds from using magic items.
There may be rare exceptions, especially with racial specific ...
They would be equally powerful, as magic effects aren't affected by caster size, only by spell level. The description of fireball says:
Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one.
[. . .]
At Higher Levels. When ...
Your player is perfectly justified in doing this. The Spider is a Tiny beast listed on page 44 of the DM Basic Rules (v0.3), or page 337 of the Monster Manual. It's CR 0, so the Druid is free to Wild Shape into it at any level (except 1st, obviously; they have to have Wild Shape).
It should be noted that there are a large number of things that eat spiders, ...
No, there are no weapon size rules in 5e beyond Heavy weapons being off limits to size small races.
There is no feature like that in the Elemental Evil Players Companion entry for the Goliath race. Powerful Build only applies to carrying capacity and the weight limits for moving things around (push, drag, or lift). There are no rules for weapon size in ...
There are guidelines for creating playable races in page 285 of the DMG, however, it doesn't go into detail on creating Large races, specifically (nor do they really go into detail on making medium characters, mechanically, save for the 'compare to other already-established races' approach). This is largely because playable races are only sized between Small ...
No, you're describing an Unarmed Attack
The game already has rules for attacking a creature using your body, rather than a weapon, and that's using an Unarmed Attack - for most characters, it deals 1+Str damage.
As the other answer points out, granting "free" unarmed attacks via body weight disrupts the intended action economy. Be careful what you wish for ...
It works just like you've been using it: the invocation doesn't care about creature size, and will make the Blast push it 10′ away. Logic agrees perfectly: it's magic and that's what it's supposed to do, so the magic does that.
There are much more powerful effects than Repelling Blast that can mess with a DM's darling plans. They're just going to have to ...
Weapon sizes are addressed in the Creating a Monster section of the DMG. On p 278 it says:
Big monsters typically wield oversized weapons that deal extra dice of damage on a hit. Double the weapon dice if the creature is Large, triple the weapon dice if the creature is Huge, quadruple the weapon dice if it's Gargantuan.
A creature has disadvantage on ...
Potions in Pathfinder may be littler than initially imagined
Popular culture frequently depicts magic potions as being of significant quantity. A Medium creature hears magic potion and may imagine something like this:
Chug! Chug! Chug!
However, in Pathfinder, the "typical potion or oil consists of 1 ounce of liquid held in a ceramic or glass vial fitted ...
I do not know of any published material from 5e yet, but there have been a book or two named Draconomicon throughout the editions. The 3.5e and 4e have rather comparable statistics, so one can reasonably assume that the 5e dragons will not be much different.
As an example, here are the average statistics for a "large" red dragon according to the 4e "...
There is no official ruling, but allowing it does not seem to be unbalanced.
As you mentioned in your question, there are no explicit rules stating how the Net interacts with being Oversized (made for something larger than Medium), and I cannot find any official statements from Sage Advice addressing it. Therefore, this is purely up to the DM.
But, for the ...
30x30 is not the limit for a colossal creature's space, its the standard. From there it only goes up.
If you look at the kaiju, you will see that colossal creatures are not limited to 30x30 space (only one of them is actually 30x30). There is even a kaiju that takes a 80x80 space.
The design of colossal creatures is so that if you need any larger stats, ...
Yes, there are rules for oversized weapons. Maybe your character can wield it, but he cannot wield it like he would be able to wield a normal sized weapon
The 5th edition DMG does have rules for oversized weapons. They can be found on page 278. The important bits are that you double the damage dice for large, triple for huge, and quadruple for gargantuan ...
From the Player's Handbook, page 147, in the descriptions of weapon properties:
Heavy. Small creatures have disadvantage on attack rolls with heavy weapons. A heavy weapon’s size and bulk make it too large for a Small creature to use effectively.
Carrying capacity has no effect on your ability to use heavy weapons without disadvantage. That's determined ...
Player's Handbook, p. 198:
A willing creature that is at least one size larger than you and has an appropriate anatomy can serve as a mount using the following rules.
However, there are limitations:
1. The DM has to say yes
It's undefined what is an "appropriate" anatomy, leaving that judgement up to the DM. It doesn't say they have to be a ...
Enlarge removes the disadvantage.
The heavy property only gives disadvantage to Small creatures.
Heavy. Small creatures have disadvantage on attack rolls with heavy
weapons. A heavy weapon's size and bulk make it too large for a Small
creature to use effectively.
A Small creature that has been enlarged by the enlarge/reduce spell is no longer Small; ...
Medium and Small characters have the same carrying capacity. Large creatures get a boost, and Tiny creatures get a reduction.
You've provided the only relevant quote yourself:
Size and Strength. Larger creatures can bear more weight, whereas Tiny creatures can carry less. For each size category above Medium, double the creature's carrying capacity and ...
In addition to the other answer, Storm King's Thunder introduces us to the magic item Potion of Giant Size.
When you drink this potion, you become Huge for 24 hours if you are Medium or smaller, otherwise the potion does nothing.
A suit of mithral armor that fits a Medium creature
The wording is indeed confusing, but the key is in the capitalization. Creature size is always capitalized. For example, the description of oil of etherealness says:
The oil can cover a Medium or smaller creature [...] (one additional vial is required for each size category above Medium).
"Isle of ...
RAW is unclear, and the tweets from Mr. Crawford are contradicting each other (and are unofficial now).
But logic, game history, balance and plain common sense dictates that Leomund's Tiny Hut is not accessible from below.
A potion of growth or an enlargement spell
By changing to medium size, temporarily, that disadvantage will go away. Both the potion and the spell make that possible.
this point got some discussion early in this edition's release. (This question is related but not identical, as is this one). This little piece of verisimilitude -- which ...
The reduced Tarrasque is Huge.
There is a subtle distinction between a creature's dimensions and its size. The dimensions of a creature are rough indications of its body's shape, whereas the size of a creature defines how much space it controls on a grid. The dimensions and size are often related, but not strictly so.
A creature's space is the area in feet ...
WotC didn't, so you shouldn't either.
There are currently no WOTC-produced player character races that are Large. I could speculate as to the reasons, but I have no designer-quote evidence to support it.
One answer to Are there any rules or guidelines for large character races? does bring up some good points, however.
What WotC did instead.
Player character ...
The 'large' ones, probably not. The 'small' ones, maybe
Is the short answer. Long answer is below:
PHB page 191 lists the the size categories, in terms of area controlled in combat, given in feet:
Tiny - 2 1/2 by 2 1/2 ft
Small - 5 by 5 ft.
Medium - 5 by 5 ft.
Large - 10 by 10 ft.
Huge - 15 by 15 ft.
Gargantuan - 20 by 20 ft. or ...