Burning Soul Feat

You harbor within your soul an ember of the flame of life that's akin to the power of a mighty phoenix. You gain the following benefits:

Prerequisite: 4th level, Wildling

• Ability Score Increase. Increase your Strength, Constitution or Charisma ability score by 1, to a maximum of 20.
• Resilient Life. You gain advantage on death saving throws. If you have Explosive Rejuvenation available when you would fail your 3rd death saving throw, it automatically activates instead. 
• You gain the Explosive Rejuvenation special bonus action (below).

Explosive Rejuvenation - Active Ability (Bonus Action, Supernatural)

• As a bonus action, you can unleash the power of the ember within your soul, exploding with fire. You regain 2d4 hit points, and all creatures within 10 feet of you must make a Dexterity saving throw, taking 2d4 fire damage on a failed save, or half as much on a successful one. The fire damage and hit points increase by 1d4 each time your proficiency increases (remaining equal to your proficieny bonus).
• Once you use this ability, you cannot use it again until you finish a long rest.

Source: KCLL, page 192

Mystic Path Feat Save DC:

• Any time a mystic path feat requires an ability score modifier for spell attacks or saving throws, use Constitution as the modifier. The DC is calculated as 8 + your Constitution modifier + your proficiency bonus.
• If your class grants you a spellcasting feature, you can use that ability modifier for calculating spell attack rolls and the DC instead of Constitution.