Hello.

Im yet a little bit noob to D&D and i dont know yet how some things work.

So, just to put a little bit of context, im creating some kind of Dwarf berserker more or less like a Slayer from Warhammer Fantassy, and i thought that making it Barbarian will be the best, but i also wanted to add a little bit of multiclassing. And i found that BloodHunter have what i want.

But here is the thing, i dont know if the Hemocraft Dice level up with the Bloodhunter class or with the overall character level, so, does someone know this?

Thanks ^^ (Also sorry if i wrote something wrong, im not english)

When multiclassing it's usually safe to assume that features from a class level up with class levels. The only exceptions are proficiency bonus (they level with character level) and spell slots (they're a whole other thing)

Thanks :)

I also found that cantrips as Thunderclap, level up with the character level instead of the class level, so i thought at first that this might be the same case.

Good point, forgot about cantrips!

Quote from Davedamon >>

When multiclassing it's usually safe to assume that features from a class level up with class levels. The only exceptions are proficiency bonus (they level with character level) and spell slots (they're a whole other thing)

This is a good an important distinction. And I agree this is the general rule. In the case of Blood Hunters, it appears Matthew Mercer leaned pretty heavy on proficiency bonus modifying class features, which is neither good nor bad--just unusual. There are several examples of this in the class.

1. Hemocraft saves scale with proficiency bonus "Hemocraft save DC = 8 + your proficiency bonus + your Intelligence modifier."
2. Reconstruction regains hit points equal to proficiency bonus.
3. Profane soul: Spell save DC = 8 + your proficiency bonus + your Intelligence modifier
4. Profane soul: Spell attack modifier = your proficiency bonus + your Intelligence modifier
5. Profane soul: "Whenever you target a creature with a blood curse, your next attack against the cursed creature deals additional damage equal to your proficiency modifier."

It never specifically says whether the hemocraft die grows along with class or character level. In the class table, there's the column for hemocraft die size and right next to it is the column for proficiency bonus. It's unclear. At my table, I would grow it based on class level.

Hemocraft dice scale with class level just like the Monk’s Martial Arts Die. 

Attack Modifiers and Save DCs always rely on Proficiency bonus for every class.

Quote from IamSposta >>

Attack Modifiers and Save DCs always rely on Proficiency bonus for every class.

 And the Profane Soul ability is exactly like Hexblade's Curse so also not unusual.