Dang. Wouldn't that be OP for a 5th level party?
Putting aside the need for silver weapons to kill it, let's say it regenerates 3 times, for 200 hp.
That assumes that your PCs are dealing 50 hp damage to it per round, so it goes down in 4 rounds.
Assuming approximately 50% hit rates, that means 100 hp worth of attacks per round.
Assuming that, on average, one PC is down per round, that means each of 4 PCs is doing the equivalent of 25 hp worth of attacks per round.
Assuming 2 attacks per round (5th level PCs with Extra Attack or equivalent), that's 12 hp damage per attack: let's say 5 base weapon, +4 from stat, +3 from sundries (I don't know the full range of 5e sundries, but I know it has various sorts of buffs available).
In 4 rounds, the monster does 8 attacks with multi-attack, +12 swipes, for a total of 20 attacks. Assuming monstrous form (which seems more exciting), that's 4 bites and 16 claws. With +9 to hit, and advantage from blood frenzy, the to-hit rate is probably close to 90%.
Each claw attack is therefore an expected 9 or 10 damage, for (let's say) 150 expected damage all-up.
Each bite is an expected 20+ damage, for another 80 all-up.
Can your PCs soak 50-ish damage per character? That will depend on their healing abilities, I think.
Anyway, that's my take on the maths. I don't have any 5e intuitions to shed any more light on it, except that I would expect 5th level PCs might be able to buff themselves into a better than 50% hit rate vs AC 16.
