Pre-requisite: kill a challenge rating 15 of higher creature.

The pride of killing that big beast has made you display your true colours evolving you into an adapted  Dragonborn. you gain the following benefits

You gain immunity to acid fire cold poison and lightning damage

your size increases to large

your base walking speed is now 40 feet

you have a flying speed of 80 feet

Your strength and Constitution scores increase by four and your charisma score increases by three

Your maximum for strength  and Constitution scores are 26 and your charisma score maximum is 24

When you are not wearing armour your armour class equals 16+ Your dexterity modifier You can use a shield and still gain this benefit

your hit point maximum increases by four and it increases by four every time you gain a level

You gain natural weapons  which are your bite which deals 2d10  piercing damage on a hit your claws which deal 3d8 slashing damage on a hit and your tail which deals 2d12 bludgeoning damage on a hit

Your  breath weapon damage die is doubled and it has a recharge of 6 rather than a rest

Your creature type is considered to be dragon not humanoid