Increase dex by 3 and con by 2

Resist fire damage

Immune to own explosive scales and resistant to other explosives.

You have explosive scales on your underside that regenerate over time. They explode after a delay or when they are damaged. Each scale does 1d4 bludgeoning damage and 1d6 fire damage. Enemies within a 10ft radius of a scale when it explodes must make a dex save DC: 12+prof bon. You can launch up to 10 scales in one round. After a long rest you have 200 scales but some don't properly explode. You regenerate 2d10 scales on a short rest.

Enemies in a 15ft cone make a dex save DC:8+ con mod+prof bon. 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.

Vulnerable to lightning and ice damage

You fly above an area and drop 30 scales in a 15ft line and then you dive down and barrel into the area causing all scales to explode and dealing 1d8 bludgeoning damage to whatever you slam into. You can use this feature 3 times per long rest.

Once hp is below 50% you enter an enraged state for 1 minute. While enraged your speed is doubled, scale explosive delay is halfed.

Once you hit level 12 you ascend to seething status. Your scales glow red and blue. Your scales explode instantly and the explosion radius is increased to 15 feet.

You have an unarmored defense of 12+dex mod