Regarding the Hive Knight **SPOILERS***

[ihyw]

So after i killed him his ghost appeared and I accidentally used the Dream Nail on him and he just disappeared . Out of curiosity, what's his monologue if you listen to him? (if any)

Does he provide anything of value to the story/game?

[Desticler]

That wasn't his ghost, that was the ghost of Hive Queen Vespa, who was happy that the Hive Knight was finally freed of his duty of defending an already dead queen.
And yes, she does provide more to the story of the game. Basically, she is the one who trained Hornet her fighting skills. She also says she is "not the queen you seek", can't go into detail on that without spoilers.

[Darc Vader]

I don't recall Hive Knight having a ghost like that, but it might have been Queen Vespa instead.

Her dialogue is

Originally posted by Queen Vespa:

My Knight... At last you are freed.

Small thing. I know your kind.

If you attempt to resolve your past then I am not the queen you seek.

It is the pale beings that bear blame for your nature.

Though this hive exists within Hallownest, we play no part in its attempt at perpetuation.

To rail against nature is folly. All things must accept an end.