I love the concept (Especially the Order of the Mutant) but it is far, far too powerful compared to all of the official material (Again, especially the Order of the Mutant).
There are exceptions, but in general each class is supposed to have two major increases in consistent offensive power: level 5 (Extra Attack) and level 11. The problem with this class is it ignores that fact and assigns major damage increases all throughout the leveling process and takes many of the damage increases from the other classes and combines them in one product (Something that should never happen: the game was intentionally designed to prevent stacking level 11 abilities - the Fighter's Extra Attack and the Paladin's Improved Divine Smite for instance. Both of which are simultaneously available in this class).
There are other, less quantifiable issues that are also pretty far out there. The Blood Curse of Mutual Suffering for example is the single most broken homebrew ability I have ever witnessed. There is no save, it is just cheap and easy guaranteed damage of a massive degree. As long as you are capable of dealing at least 50% of the damage your enemy is (Something that is almost certain considering the incredible damage output of this class), you are certain to win any 1v1 fight regardless of other conditions. Turning the randomness of battle into certain victory is poor design - it takes away all risk and makes the game boring to the extent that no-one should even want to play it anymore. You need to add some drawbacks to the ability like a saving throw, and considering how incredibly powerful the ability is, make that save check often. Simply making it require concentration would work.
Just to clarify what I mean about the general imbalances, I'll highlight just what sort of damage this class brings to the table, and compare it to other options.
Take this simple build: Barbarian 2/ Blood Hunter (Order of the Mutant) 18, with 20 base Str, a Greatsword, using Crimson Rite, Blood Curse of the Marked (Mutual Suffering is clearly better but harder to quantify in such comparisons), Rage, Reckless Attack, and the following Mutagens: Cruelty, Potency, and Precision.
Against AC 18, all of that will inflict 105.12 DPR on average, without using any feats.
The top dog of damage in a non-homebrew game is the level 20 Berserker Barbarian with 24 Str, a Greataxe, using Rage, Frenzy, Reckless Attack and Great Weapon Master.
Against AC 18, all of that will inflict 73.4 DPR on average, at the cost of 1 feat and a level of exhaustion.
This class does 43.22% more damage without bothering to enhance his damage with feats, than what the previous king of damage can pull off when going balls to the wall. Creating a new king of damage by making something that does more damage than everyone else is kind of dubious but not terribly bad, but crowning a new king by such an absurd margin is simply unacceptable.