Kobolds, Dragonborn, and Dragon Shifters

The Kobolds of Avaria don't just claim to be descended from dragons, they know they are. To be more specific, the Kobold species--and its offshoots, Dragonborn and Dragon Shifters--are the result of the answered prayer of an Ancient Copper dragon named Avasitarien, who lived her whole life among the humanoid and anthropoid peoples, despairing of the dragons' implacable hatred for their own kind.
Kobolds--the beings who resulted from her request of the goddess Refuge--lay eggs in clutches of 8-20 about once a decade. When the eggs hatch, the babies that come out are desperately hungry, and immediately attack each other, the stronger ones killing and consuming the weaker until every survivor has taken at least one of its siblings' lives. Only after this first kill do the young Kobolds begin to recover from their frenzy and develop the beginnings of sentience. Most don't have any conscious memory of their birth feast, but many outsiders suggest that unconscious remorse for it is behind the Kobold species' much remarked upon love for "adopting" any and all strays and orphans, of any species. Kobolds don't experience such mindless blood-lust again.
However, a Kobold who lives to be 99 or 100 years old begins to feel a very similar hunger bubble up from within themselves. It's controllable this time, recognizable and expected. They begin to gorge themselves on meat, as rare as they can get it, for several weeks to a month, and then fall into a torpor deep enough to call a coma, for about a week, after which they wake up having grown into a medium-sized version of themselves: a Dragonborn. In about one in 20 cases, the newly developed Dragonborn has lost all memory of their previous century of life as a Kobold. (Including any class levels they had.) These "clear minded" Dragonborn almost always leave their former home, where everyone calls them by an unfamiliar name and claims to know them, striking out for a new area where they will be as new to others as everything is to them. Many new Dragonborn who didn't lose their memories also choose to relocate after this great adjustment in life, taking it as an indicator that it's time for a change (and also maybe a home with higher ceilings).
Dragonborn as a group tend to be much more introverted and standoffish than Kobolds. With the change they lose the ability to reproduce, and are usually given the honorific "Essa" among Kobold communities, rather than sir or ma'am. There are superstitions and rumors that Dragonborn who live for 200, 400, or 500 years more may go through another change, becoming something even more similar to their draconic ancestors. But elderly Dragonborn are few and far between, and no proof for or against this claim is generally known.
Occasionally, one of the babies in a clutch of Kobold eggs has wings. These winged Kobolds are no different from their siblings otherwise, as they grow and develop, but should they survive to the end of their first century, and go through the change as described above, they become what are known as Dragon Shifters.

Kobold Species:

Age. Kobolds reach adulthood in 16 years and can live to 100 (see above).
Size. Kobolds stand just three to four feet tall and weigh perhaps 40 pounds. Your size is Small.
Darkvision. Kobolds have superior vision in dark and dim conditions. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.
Dragon's Armor. Your skin is covered in a layer of small but sturdy scales. When you aren't wearing armor, your AC is 13 + your Dexterity modifier. You can use this natural armor to determine your AC if the armor you wear would leave you with a lower AC. A shield's benefits apply as normal while you use your natural armor.
Dragon's Scales. Kobolds reflect their draconic heritage in their coloring, bearing either one or two of the colors of a classic dragon in their scales. How they blend is up to you: sometimes they intertwine in patterns like stripes, spots or blotches, sometimes one is the primary tone and the other merely an accent along the edges of the scales (colloquially called a "net"), and sometimes they're literally blended to form another shade, like a red and white Kobold having pink scales. Choose or roll twice on the following table to determine your colors, and the associated elemental resistances you have. If both of your draconic colors share the same resistance, then you instead have immunity to that element.

1d10	Scale Color	Element	Area
1	Gold	Fire	Cone (Dex.)
2	Silver	Cold	Cone (Con.)
3	Bronze	Lightning	Line (Dex.)
4	Brass	Fire	Line (Dex.)
5	Copper	Acid	Line (Dex.)
6	Red	Fire	Cone (Dex.)
7	Blue	Lightning	Line (Dex.)
8	Green	Poison	Cone (Con.)
9	Black	Acid	Line (Dex.)
10	White	Cold	Cone (Con.)

Variant: Winged Kobolds About one in ten kobold hatchlings is born with large, functional, bat-like wings. Because of the delicacy and awkwardness of these extra appendages, their survival rate is somewhat lower than that of their wingless clutch-mates, but enough do make it to adulthood for a flying Kobold to cause no great outcry when seen. To play a winged Kobold, replace the selection of a second scale color with the following trait:
Dragon Wings. You have large functional wings that grant you a flying speed of 50 feet, with the following limitations: At 1st level, you can use your wings only to glide, achieving up to 10 feet of forward movement for each 1 foot you descend. After making a glide of two rounds or more, you cannot glide again until finishing a short or long rest. At 3rd level, you can use your wings to fly for up to ten minutes, in one minute increments. After that much use, you must complete a short or long rest before you can fly any more. At 5th level, you can use your wings to fly for up to one hour, in one minute increments, after which you must complete a short or long rest before you can fly any more. At 7th level the only limit on your flight time is the rules on travel and exhaustion.
To use this speed, you can't be wearing medium or heavy armor.

Dragonborn Species:

Age. Dragonborn come into being when a Kobold reaches 100 years old and goes through the change, so they are considered adult as soon as they recover from their torpor. There is no upper limit to a Dragonborn's age known, and they show no particular signs of aging as time passes.
Size. Dragonborn are tall and bulky, standing between 6 and 7 feet and weighing around 250 pounds. Your size is Medium.
Darkvision. Dragonborn have superior vision in dark and dim conditions. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.
Dragon's Armor. Your skin is covered in a layer of small but sturdy scales. When you aren't wearing armor, your AC is 13 + your Dexterity modifier. You can use this natural armor to determine your AC if the armor you wear would leave you with a lower AC. A shield's benefits apply as normal while you use your natural armor.
Dragon's Scales. When a Kobold goes through the change, their scale color shifts, simplifying from two draconic shades to one. They lose the resistance associated with the lost shade (or their immunity drops to resistance if they had only one).
Dragon's Breath. You can use your action to exhale destructive energy. Your scale color determines the size, shape, and damage type of the exhalation, as seen on the chart above.
When you use your breath weapon, each creature in the area of the exhalation must make a saving throw, the type of which is determined by your draconic ancestry. The DC for this saving throw equals 8 + your Constitution modifier + your proficiency bonus. A creature takes 2d6 damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level.
After you use your breath weapon, you can't use it again until you complete a short or long rest.

Dragon Shifter Species:

Age. Dragon Shifters come into being when a winged Kobold reaches 100 years old and goes through the change, so they are considered adult as soon as they recover from their torpor. There is no upper limit to a Dragon Shifter's age known, and they show no particular signs of aging as time passes.
Size. Dragon Shifters are tall, with relatively slender builds, standing 6 to 7 feet and weighing around 180 pounds in their draconic form. Your size is Medium.
Darkvision. Dragon Shifters have superior vision in dark and dim conditions. You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray.
Dragon's Scales. You still have the single draconic scale color you were born with, and the resistance that goes along with it. When creating a new Dragon Shifter, roll or choose it from the table above.
Dragon's Wings. You have large functional wings that grant you a flying speed of 60 feet, with the following limitations: At 1st level, you can use your wings only to glide, achieving up to 10 feet of forward movement for each 1 foot you descend. After making a glide of two rounds or more, you cannot glide again until finishing a short or long rest. At 3rd level, you can use your wings to fly for up to ten minutes, in one minute increments. After that much use, you must complete a short or long rest before you can fly any more. At 5th level, you can use your wings to fly for up to one hour, in one minute increments, after which you must complete a short or long rest before you can fly any more. At 7th level the only limit on your flight time is the rules on travel and exhaustion.
To use this flight speed, you can't be wearing medium or heavy armor.
Second Skin. As an action, you can polymorph into one Medium sized humanoid or anthropoid form, chosen at character creation. This is a specific appearance, recognizable as an individual, and chosen from all the other available playable Medium sized species. Your Ability scores remain the same in either form. While in your non-draconic form you lose access to your Dragon's Scales and Dragon's Wings traits, but gain all the species traits of your second skin form. Any equipment you are wearing or carrying isn’t transformed. You revert to your winged draconic form if you die.

Kobold, Dragonborn, and Dragon Shifter Common Cultures:

Members of the draconic races are most commonly found in Avaria, so are frequently In the Heart of Avaria for culture as well, but the majority of the continent is lightly populated and peaceful, so Small Farming Settlements are very common, and Walled Townsfolk somewhat less so. Residents of any of the four major cities are of course likely to be City Dwellers.

Kobold etc. Languages

Avarian is the native language of Avaria, a descendant of Draconic. It has a coughing, consonant-heavy sound rather at odds with the affable nature of most of its speakers. Other languages commonly spoken in the Kobolds' nation include halfling, dwarven in the mountainous western portions of the continent and Na'atene in the eastern portions.
Suggested Heritages: Shifter Heritages are unheard-of in Kobold-kind, their own life stages apparently being enough of that, but any other heritage is possible.