Multiple Heads. The hydra has six heads. While it has more than one head, the hydra has advantage on saving throws against being; charmed, deafened, frightened, stunned, unconscious and when it sleeps one head is always wake as will as it can’t be surprised. It also gets a reaction for each head. Being blind the Hydrazi is immune to anything involving or needing the ability to see.

Whenever the hydra takes 35 damage in a single turn, one of its heads dies. If all its heads die, the Hydra will lie dormant. If it does loose all of its heads or it’s health drops to or below zero, it will regrow a head every 1D4 rounds until it has at six again.

At the end of its turn, it grows two heads for each of its heads that died since its last turn. The hydra regains 20 hit points for each head regrown in this way.

Death: The only way to kill the Hydrazi is to remove its heart from it’s chest. Not an easy task since it’s chest is as hard as iron. Once it’s heart is removed, the Hydrazi has 1D4 rounds to get it back it in. Once that ends it makes DC 16 Con saves until it fails, once it does it will die.

Multiattack. The hydra makes as many bite attacks as it has heads.

Bite. +11 to hit, reach 30 ft., one target. Hit: 10 (1d6 + 5) piercing damage. Plus 1D6 narcotic on a successful attack.

Breath Weapon (once every 1D6 rounds):  A 10 ft cone 60 ft long of narcotic damage 5D6. DC 16 Dex save, on a successful save half damage and on a fail full.

Angelic Voice:  the Hydrazi can use one of its heads to sing a hypnotic song, heard up to 1/mile. On a DC 21 Perception check adventures will notice the song on a  DC 18 investigation once the song is heard they can figure out the direction it’s coming from. Once in range of the song a failed DC 17 Wis save the adventurers will have disadvantage on all Charisma and Wisdom based saves. And if immune they become susceptible to these.

Spell like abilities: spells cast at caster level 14

1/Day: Counter Spell as a reaction, Hypnotic Pattern, Greater Invisibility, Hallucinatory Terrain, Major Image, Weird

at will/ Minor illusion, Disguise Self on each head, invisibility on a target spot of its body like a neck or a head.

The Hydra can have multiple heads and it gets a reaction for each one. 

1/Day can cast Counter spell as a reaction

3 per round, after each turn

Regrow: can sprout two new heads from a dead one

Breath Weapon: as described above 

Reach: move one of its heads up to 100 ft to a max of 250 ft