Ghosts of Saltmarsh - homebrew warlock captain

Hey, this is my first time homebrewing a monster. Could I have some thoughts and feedback on him? Margrave Dain (the Grinning Captain) - Monsters - Homebrew - D&D Beyond

I'm running a Ghosts of Saltmarsh campaign. It's been super fun so far. I'm kind of cherry-picking the adventures and then also weaving in some arcs based on the player characters. One PC escaped a slaver before they came to Saltmarsh, so I created this guy and I'm hoping he will end up as a mini boss for the party.

Does CR 8 feel right? Does he feel balanced? I think he's a bit of a glass canon at the moment, but unless isolated he will also have crew.

It looks good, and reasonably balanced, but there are a few issues.

• The AC is incorrect. Hide armor would give either 14 or 15 AC (can't remember if it's plus 1 or 2).
• What spell slots are recharging on a short rest?
• The multiattack should be 3 attacks.
• The average damage of Eldritch blast is 9 per beam, making it vastly inferior to the other options.
• Grasp of the Deep should clarify whether or not it can grapple creatures that enter the area.
• The eldritch blast legendary action is just awful. 2 actions to do barely half the damage that can be done with one.
• Fathom Pull is fairly underwhelming. The distance should be increased.

Quote from Maruntoryx >>

It looks good, and reasonably balanced, but there are a few issues.

• The AC is incorrect. Hide armor would give either 14 or 15 AC (can't remember if it's plus 1 or 2).
• What spell slots are recharging on a short rest?
• The multiattack should be 3 attacks.
• The average damage of Eldritch blast is 9 per beam, making it vastly inferior to the other options.
• Grasp of the Deep should clarify whether or not it can grapple creatures that enter the area.
• The eldritch blast legendary action is just awful. 2 actions to do barely half the damage that can be done with one.
• Fathom Pull is fairly underwhelming. The distance should be increased.

 This is super helpful feedback, thank you!

Updated version here! Margrave Dain (the Grinning Captain) - Monsters - Homebrew - D&D Beyond