What do you think about Neheb, Dreadhorde Champion ? It works very good for ramp and fixing only your hand

Neheb is a pretty hefty mana investment when typically you want to be holding up mana for interaction in a deck like this.

I like Sigil of Sleep and/or Basilisk Collar a lot . Well this depends on your meta, it's more casual i think.

Yeah I think they would fit more into a casual meta. Those cards are only really usable if Niv is already out, and if he's out the focus should be on winning the game. If those cards were instead draw/dig spells, they'd get you a draw, be more useful throughout the game, and give you the ability to hunt for a game winning card.

Last question :) what do you think about Pirate's Pillage for Captain Lannery Storm . It is one mana more but guaranteed 2 treasure tokens (sometimes you don’t get good attacks or get it removed after first attack) and you draw two cards (-1) with a sorcery that synergies with your commander as well (also with Glint-Horn Buccaneer, Dig Through Time, Narset's Reversal, Baral, Chief of Compliance)

In full cedh games, its much more likely to get good attacks with Lannery. I can't remember the last time I didn't have someone to attack. I would also easily swing her into someone with a Tymna out because they'd be extremely unlikely to block. She almost always generates 2+ treasures.

Pirate's Pillage might actually probably be playable if it wasn't a Sorcery (I wish it was an instant) Tapping 4 at sorcery speed is a huge risk, so the rewards needs to match that. Treasonous Ogre and Stranglehold do that, but I don't think this does.