Giant Subrace

Ability Score Increase. Your Constitution score increases by 1.
Explosive Growth. Starting at 3rd level, you can use your action to unleash the infinite energy within yourself, causing your body to explode in both size and power.
Your transformation lasts for 1 minute or until you end it as a bonus action. When you first transform, each creature other than you in a 10-foot radius centered on you must succeed on a Dexterity saving throw or take a number of d6s of fire damage from the explosion equal to your proficiency modifier.
During the transformation, you shed bright light in a 30-foot radius and dim light for an additional 30 feet. Your size expands, you become Large. If there isn't  enough room for you to expand your size, you attain the maximum possible size in the space available. In addition your melee attacks deal additional damage equal to your proficiency bonus.
Once you use this trait, you can't use it again until you finish a long rest.