Fell Alter

Fell Alter

Once per long rest, the first time you would drop to 0 hit points as a result of taking damage, you can choose to relinquish control of your body over to your Fell Alter. Instead of rolling death saves, you roll alter saves. Alter saves are used to determine whether or not you maintain control over your Fell Alter. Similar to death saves, alter saves aren't tied to any ability score and are aided only by spells and features that improve your chances of succeeding on a saving throw.

Roll a d20: If the roll is 10 or higher, you succeed. Otherwise, you fail. A success or failure has no effect by itself. On your seventh success, you become stable. On your seventh failure, your Alter gains complete control over you. The successes and failures don’t need to be consecutive; keep track of both until you collect seven of a kind. The number of both is reset to zero when you regain any hit points or become stable.

Rolling a 1 or 20: When you make an alter saving throw and roll a 1 on the d20, it counts as two failures. If you roll a 20 on the d20, it counts as three successes.

Damage at 0 Hit Points: If you take any damage while you have 0 Hit Points, you suffer an alter saving throw failure. If the damage is from a critical hit, you suffer two failures instead. If the damage equals or exceeds your hit point maximum, you suffer instant death.

While your Alter is unleashed, you gain the following features:

Bloodflame Rebuke

You have a pool of damaging power equal to a fourth of your hit point maximum, rounded down. Whenever you hit a creature with a weapon attack, you can choose to draw power from the pool up to the maximum amount remaining in your pool to deal additional fire damage to the target. Once the pool has been used, it is replenished whenever you unleash your Fell Alter again.

Bloodflame Frenzy

While your Fell Alter is active, as a bonus action, a nonmagical weapon you touch becomes imbued with bloodflame. The weapon has a +1 bonus to attack rolls and deals an extra 1d4 fire damage. A creature struck by a weapon imbued with bloodflame must make a Constitution saving throw equal to 10 + half your character level or have their hit point maximum reduced by an amount equal to the fire damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0. 
This feature ends if the weapon is more than 5 feet away from you for 1 minute or more. It also ends if you use this feature again, if you dismiss the bloodflame (no action required), or if you die.

Frenzied Strikes

Whenever you hit a creature with a weapon imbued with bloodflame, you can expend 5 points from your Bloodflame Rebuke pool to make another attack using the same weapon. 

Crimson Slash

As an action, you create an illusory black blade, then leap forward to deliver a spinning slash that emits a wave of bright light in a 10-foot radius and dim light for an additional 10 feet. Make a melee weapon attack against a creature you can reach using a weapon imbued with bloodflame. On a hit, the target takes 4d6 necrotic damage. A creature afflicted by the necrotic damage must make a Constitution saving throw equal to 10 + half your character level. On a failed save, the creature has its hit point maximum reduced by an amount equal to the necrotic damage taken and takes 1 point of fire damage at the start of each of its turns. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.
Immediately after using this attack, you can expend 10 points from your Bloodflame Rebuke pool to make an additional weapon attack as a bonus action.
This feature can only be used once per Long Rest.