Good or Evil: intelligent creatures can make moral choices
The alignment specified in a monster’s stat block is the default. Feel free to depart from it and change a monster’s alignment to suit the needs of your campaign. If you want a good‑aligned green dragon or an evil storm giant, there’s nothing stopping you (Basic Rules, DM, p.3/ MM p. 7).
Disclaimer: This answer was written before the addition of the 5e tag. The content below may not be applicable to that specific edition of D&D.
D&D 3.5's Draconomicon actually has several examples of dragons having specific smells. It seems to vary by dragonflight color:
Black - Smells like rotten vegetation and foul water.
Blue - Smells like ...
No, Drakes aren't Beasts
Drakes, though animal like in appearance and behavior, have the creature type of dragon, not beast. And the Ranger's Companion states:
Choose a beast that is no larger than Medium and that has a challenge rating of 1/4 or lower (PHB, p. 93 bold added).
"Beast" is not just a descriptive word here, it is a creature type (see ...
It is very good storytelling.
One of my top tips for DMs is, if you can shove player's past into the mix and make it look flawlessly pre-meditated, the players will adore you. It is always good to have the player's backstories come haunt them enough to push them into action but little enough as to not make an entire campaign centered around two of these ...
The plan should not work due to the word game being played
You are inflicting something similar to progeria on the young dragons
Growth and maturation, and aging, are not direct synonyms. (Example: I have never stopped increasing in age, but I stopped growing taller in my mid to late teens, and I was full grown/developed somewhere in my early twenties).
I would treat this as if the sorcerer had cast True Polymorph (another 9th level spell) and concentrated for the entire duration to make the transformation permanent. Since you subjected the sorcerer to great additional risk to use Wish to become a dragon (and the sorcerer really wished to be a dragon) you should treat this as a change in reality rather than ...
There are three somewhat-contradicting definitions of True Dragon, from Monster Manual, Draconomicon, and Races of the Dragon (listed by publication date).
Please also note my other answer, which poses a rebuttal that I’ve come across.
The first definition, in the Monster Manual, is simply the “Dragon, True” entry, which ...
Green dragons have never breathed fire in D&D
Various fantasy artwork, both old and recent, has depicted a green dragon who breathes fire. This is generally because in some myths, including those which inspired D&D's conception of the creature, dragons are imagined as reptilian, who are often green; and in some myths and stories, including The ...
A dragon's breath shouldn't be able to pass through
I agree with other answers that RAW a dragon's breath can pass through the Hut.
However, I believe that in this case, sticking to a RAW ruling can hurt your game.
In any other situation, the Hut prevents just about anything, any attack from passing through. The dragon breath is an edge case that ...
As intelligent NPCs, dragons will have a range of personalities and motivations; however, since your trouble is with separating them from ordinary humanoid NPCs, I would recommend playing up the stereotypes a bit to add some distinction.
I will draw mostly from Draconomicon here, since the specified system is 3.5. It has some advice on roleplaying dragons, ...
A unique and highly unusual new dragon offspring, who is typically sterile
The D&D 3.5 sourcebook Draconomicon (2003), p.27 asserts that dragons of different types can produce hybrid offspring:
Crossbreeds between dragon species are not unknown, but very rare. A hybrid dragon of this sort is usually left to fend for itself, but on occasion both ...
It’s a problem but perhaps not as bad as “ECL 5” suggests
You are probably more powerful than a 1st-level character should be. You are not, however, as powerful as a 5th-level character can be, or even should be. Moreover, even as a 1st-level character, Wyrmling White Dragons have some glaring weaknesses that don’t seem appropriate.
The LA system is poorly-...
It All Started With Gold Dragons
The first dragons able to change shape into human form were Gold Dragons. None of the others could. On pages 11-13 of Monsters and Treasures (OD&D, 1974, TSR) there were a total of six kinds of dragons: red, blue, white, black, green, and gold. The only metallic dragons in the game were described as "being a class unto ...
An elf is not immune to the Dragon's Sleep Gas
Jeremy Crawford has clarified in a tweet that Fey Ancestry only protects against magical sleep.
Nonmagical sleep gas/poison/etc. can knock an elf unconscious, unless its description says otherwise.
He also clarified in another tweet that a Dragon's breath is not magical.
The breath weapon of a typical dragon ...
Dragons cannot upcast innate spells
The MM says this on innate spellcasting (p.10):
Unless noted otherwise, an innate spell of 1st level or higher is
always cast at its lowest possible level and can't be cast at a higher
This is not circumvented by the rules for dragons (p.86)
Each spell [..] the spell’s level can be no higher than one-...
To address the second part of your question, from the 5e Monster Manual, page 7:
The alignment specified in a monster's stat block is
the default. Feel free to depart from it and change a
monster's alignment to suit the needs of your campaign.
If you want a good-aligned green dragon or an evil storm
giant, there's nothing stopping you.
At least ...
A general rule of storytelling is that you can go wild with unlikely random coincidences to set up the story (first act), but while the story is progressing (second act) they should be used more sparingly. The finale of the story (third act) should be the logical and deterministic conclusion of the events which happened before.
Unlikely circumstances are ...
The undead shadow is literally the humanoid's actual shadow, turned into an undead monster. It is not the humanoid's soul itself.
The Monster Manual entry for the Shadow states:
If a creature from which a shadow has been created somehow returns to
life, its undead shadow senses the return. The shadow might seek its
"parent" to vex or slay. Whether ...
CR ignores versatility
I will preface addressing the two "extra" abilities the Gold Dragon has over the Red Dragon by saying that the CR calculation described in the DMG ascribes no value whatsoever to versatility. The main way that you calculate the effect a monster's battlefield impact has on its CR is its damage:
If a monster has different ...
By canon, as your question asks, nope.
First we'll define the word canon so we're clear about what we're discussing as it applies here, I'll leave out definitions that don't apply:
a general rule, law, principle or criterion by which something is judged; or
a collection or list of sacred books accepted as genuine (or the works of a particular author ...
Let's take this feature at a time...
This is just flatly wrong. This class is a half-caster, they should not prioritize their casting stat. Glancing down below, this class would always want to prioritize Dex--they are restricted to Light Armor no access to the Mage Armor spell and they don't have Cantrips for steady damage output. So they'll ...
The Dragon Needn't Be a True Dragon
As Aaron's answer indicates, dragons that have appropriate CRs for the party will be at most Medium. Although that means the dragon could be, potentially, the size of a professional wrestler, for a dragon that's sort of... unimpressive.
I suggest the following.
Use a creature that could be mistaken for a dragon
The lowest-CR drake on D&DBeyond has CR = ½
A ranger's companion must have CR ≤ ¼.
So no, you cannot (currently) have a drake as your animal companion. To do so would require either a modification to the ranger rules or a new drake with CR ≤ ¼ (and the beast type, as gandalfmeansme rightly points out) to be published by WotC.
There's no specific prohibition against applying the half-dragon template to a dragon.
However, applying templates to monsters is DM business. It's not something that will happen just randomly out of nowhere, or by a player's initiation — templates are tools, and most exist only to get a job done as needed by a DM. A DM who needs to make a half-dragon ...
Lair actions and regional effects are only permitted to legendary creatures.
From page 11 of the MM:
A Legendary Creature's lair
A legendary creature might have a section describing its lair and the special effects it can create while there, either by act of will or simply by being present. [...] This section only applies to legendary creatures that ...
BBEG's plan won't work as written
One fatal flaw to this plan is the BBEG is unable to create dragons like this.
True polymorph says:
Creature into Creature. If you turn a creature into another kind of creature, the new form can be any kind you choose whose challenge rating is equal to or less than the target's (or its level, if the target doesn't have a ...
Any dragon of CR 21 or greater could potentially know Plane Shift innately
The "standard" spell for crossing into arbitrary planes is Plane Shift, a 7th level spell. Any dragon that could cast this spell would be able to use it to access the Feywild. The Monster Manual's section on dragons presents a variant titled "Dragons as innate spellcasters", which ...
Time travel to the past instantaneously then time travel to the future conventionally
A magic portal can be created that transports its users to the past (and only to the past). Such a portal is created by a caster using the 9th-level Sor/Wiz spell teleport through time [conj] (Perilous Gateways Web column "Portals in Time: The Portal through Time (Part 2)")...