Alright here is my review:
My first note, I'm not sure how much you are putting into the statblock directly vs leaving as like dragon intro text, so I'll make notes of what I think should go in the statblock.
I don't think any of this is going in the stat block, except a reference with a hyperlink. This is all supplemental information for people who want more detail / options for their dragons.
Also, thank you for taking the time to review and comment!
Dragon Fear
I think we can tighten this up to more normal 5e language, we can probably take out the special notes about flying overhead and just make the dragon's fear effect has a large radius (because why not, dragon fear is a key ability of the creature). So here's a version below:
Aura of Menace
This ability effects all creatures within 150 feet (this value increases depending on the specific statblock) that have CR/level equal or less than half the dragon's CR. Such creatures are automatically frightened. While frightened, the creature must use the dash action and spend all of its movement to move away from the dragon. After 1 minute the creature must make a DC X Wisdom saving throw to end the effect, repeating the save every minute until successful. This save is made at disadvantage if the creature can see, hear, or smell the dragon. Once the save is made, the creature is immune to the ability for 24 hours.
The dragon may choose creatures to be immune from this effect (this is to allow for dragon servants)
Frightful Prescence
The dragon can apply its Aura of Menace against creatures whose CR/level is equal or less its CR. These creatures get an immediate saving throw, and may make a new one at the end of each turn until successful.
I like the idea of simplifying it. The plan was to keep Frightful Presence as is and this just augments / give more context. I will think about how to clean it up.
Dragon Armor
I like this block a lot because its such a common question whenever my players kill a dragon. I do want to check if the armors are supposed to allow a dex bonus....they are noted as medium armor which normally does allow it. I do think the higher shields are really good, +3 is basically a legendary shield...and shield bonuses when stacked with magical armor as well tend to create ACs some consider outside bounded accuracy.
I did a little be of comparing to the official crafting rules, but not to much. The bonus are intended to be exceptional as you have kill a at least CR 26 wyrm to or mythic great wyrm to get them. But I'm sure it could be tweaked for more balance, but I am not sure that is the point. At some time I will loot at more. FYI, you might want to look at
Monster Loot on the DMs Guild it gives information like this for all the monsters. The dragon entries include info for claws, fangs, wings, lungs, and glands (for making breath weapons). This is based somewhat on that work, but I didn't want to go into that much detail. Though dragon teeth should probably get an entry.
Dragon Hoard
I don't know if the values are "good" (I don't usually use treasure tables myself), but I really like this note and inclusion.
The tables in the DMG only go up to 17+, so every add on is more treasure than suggested in the DMG.
Dragon Tactics
Shaped Breath: Its a good ability, but its not that strong for what seems to be the capstone of dragon tactics.
It is just flavor for good dragons really, I don't see a lot of evil dragons caring to use this trait.
Strafing: So we need to add some language to handle cones. I would say something like. For cone breaths, the width is equal to the normal length of the breath.
That language is already in the definition of cone I believe. Though I am planning on including a sketch instead of more text.
Sustained Breath: I think you can go a few ways with this. The simplest way is to simply say "3 Legendary Actions: The dragon automatically recharges its breath weapon". However, if you want this to be more of a sustain, I think its got to have some kind of "lingering effect".
I think that language is confusing as that is not what I am going for - it is specifically not a recharge. However, I will think about simplifying it. For the math to work I need it to take the dragons action and all its legendary actions on both turns. I just wasn't sure of the best way to say that.
Snatch and Throw: So it seems I am giving up my claw attacks for an auto throw if I get in my bite. The damage tradeoff doesn't seem that great, I guess there is the benefit that many creatures wouldn't be able to get in a melee attack routine afterwards....so maybe, I'd have to see it in play.
Options, that is the important thing. The key for most of these options are that they are things the dragon should be able to do if it wants, even if it doesn't make sense from a DPR perspective. I just want to give DMs options for a memorable battle. Also, once you throw the poor fighter at the mage on the back line, it starts to even out damage wise.
Dragon Flight
Ultimately I think this is way too fiddly and complicated. I think we can greatly simplify this.
Overland Flight: If a dragon is not engaged in an encounter and is moving in a straight line, they can move 10 times their normal fly speed.
Your absolutely correct, I over thought this one. I still might keep some of it, but much to complicated at the moment.
Crush: Is the intention that this would be your action?
Yes.
Dive: This one seems needless with the other fly options.
I almost deleted it, but it seemed like something a dragon should be able to do in aerial combat, so I kept it. The important thing I think is the stunning aspect, as the victim would start falling.
Stall: A bit too complicated. First I think we just add this into the multiattack options instead of limiting its specific attacks. And then simplify the effect:
"Wing Buffet: The dragon must be flying and this action consumes X amount of movement. All attacks against the dragon are at disadvantage, and the dragon gains +5 AC against ranged attacks. If the dragon is within 10 feet of the ground containing loose dirt and debris, than all creatures within 150 feet (scaled based on fear aura) make a DC X con save or become blinded. All effects last until the start of the dragon's next turn."
Thanks, that is a lot better.
Lair Actions
I really like the clairvoyance idea, simple and cool.
I got the idea from the 2e dragon write up.
Red Dragon: Magma Eruption - The effect is fine but the flavor is a little off. If its a pillar of "fire", than the damage is fine. But the damage is too low for "lava"... so I would just update the flavor text slightly to be more in line with the damage.
It was called magma eruption in the MM, but I thought the lack of bludgeoning damage seemed of for magma. I have not issue with the amount of damage though. I will probably just change the name to something fire related. The regional effects include fissures to the plane of fire so that makes sense.
Blue Dragon: They are described to live in deserts not caves, so cave in is ann odd ability.
Desert caves I guess? This straight from the MM. However, I to thought it a bit odd and think it best to change it. Any suggestions?
Green Dragon: The wall of thorns may be really strong at the mid CRS when mobility is still a bit limited.
This is pretty much straight from the MM, other than age category increases. I am open to improving though (or replacing it).
