You have found your blood flowing hot as boiling water even when you are relaxing, so much so that even your wounds don’t scab over but instead cauterize themselves with a sizzling sound. Your veins seem to glow lightly, as if lava is flowing in them. To make things worse any amount of activity or change in your emotions only seems to make it hotter and hotter. Will your body hold?
Overheating
You have a maximum capacity of Heat equal to your proficiency bonus. You can generate Heat to trigger your various abilities, and they are reduced back to 0 on a long rest. When you reach that cap you can still use your abilities by going past it, as your body attempts to keep you from burning up. You take 2d8 fire damage per Heat above your cap whenever you activate an ability in this way, which ignores any resistances and immunities you may have.
Additionally the more Heat you generate, the more harsh, intense, easily irritated and even violent you become, the changes becoming more apparent as you reach and surpass your Heat cap. You can’t help but fear that some of them might become more permanent.
Heat Aura
Your body constantly emits heat around you. Any item you touch that can fit in 1 cubic foot begins to get warmer by 1 degree per round as long as you remain in contact with it. You may instead touch objects or surfaces larger than that but you only heat up 1 cubic foot at a time. This can cause flammable items to erupt into flames and liquids to evaporate. Due to this you can’t carry potions as they tend to turn into vapors inside their bottles, unless your insulate them in a way that requires at least 1 action to unpack.
Magmatic Heart
As a bonus action you can tap into the magic of the everlasting furnace that has become your heart, gaining some control of your blood. You gain resistance to fire damage for 1 hour and generate 1 Heat.
Additionally you are immune to any negative effects from hot temperatures.
Fired Up
Whenever you fail a saving throw you may as a reaction attempt to push past your body’s natural limits by expending one of your Hit Dice to roll it and add it your total. This generates 1 Heat.
Additionally, when taking the Attack action you can generate 1 Heat to cause your attacks for that action to deal additional damage equal to your total Heat.