Hatorade
A nice asshole.
I just watched the hunting horn guide video thing earlier today since I was thinking about it, it does look pretty cool, like a non shitty hammer tbh, and the songs look pretty OP even for solo play.
There's not many attacks for the hunting horn though. There's a bunch of holding back while doing something to get another hit, and the big hit is when you do an encore, which is play a song then play the same song again right after, the encore does devastating damage so that was probably that. I think you just R2 again, or hold it not sure, it'll do a bunch of powerful attacks then play the same song again(so it maxes it at lvl 2).
Watch a HH tutorial vid, you got enough wrong to be confusing what does what.