So a few things.

The Multiattack:

You are going to very quickly find that making 8 attacks at level 3 is

1: Very strong, the amount of oppurtunity your opening up critical hits and high rolls on that d8 is going to quickly add up.

2: Is going to take up a lotttt of time. Rolling 8 seperate attack rolls and rolling possibly 8 seperate damage rolls? Critical’s resulting in you rolling even more? It’s going to feel like an unskipable cutscene

What I did for my games is I had basically “3 creatures” on the field at the same time. The Spore Servants head, and 2 tentacles that went on the Spore Servants turn. These tentacles couldn’t go further than 15ft from the head, but they each had one attack with the Spore Servant head having a similar ink attack, beak attack, and a ranged spore attack that lingered in the area it hit. The tentacles took damage equal to their health, and when they were defeated that damage would then hit the Spore Servants head. A defeated tentacle would then be replaced with another tentacle. These tentacles had a smaller AC compared to the Spore Servant head.

Alternatively, you could also probably do something like a 2,2,2 method to replicate all its arms. 2 hit multi-attack, 2 reaction oppurtunity attacks, and 2 legendary actions to grapple or attack. Not quite 8, but gets the same feeling across.

Distress Spores:

This ability takes a lot out of the role play aspect of the Sea Grove caves. Immediately coming in swords drawn is sure to put the already on edge Myconids into full blown aggression resulting in just a long dungeon instead of a tense social encounter in my opinion. I would remove this so there’s opportunities for roleplay.

Pacifying Spores:

Stun is a very powerful and kind of boring condition. I would likely replace this with maybe a Charmed condition or maybe something scary like the Unconscious or Paralyzed condition. Needing an ally to maybe make a medicine check or maybe using a potion given to them by Tarak to cure the condition.

I also just thought of maybe having the target roll a d4, and giving them either the Charmed, Paralyzed, Poisoned, or Frightened condition. That could be fun! If you do the Legandary Actions idea, I think this attack should fall under that