You Want That? Nah.

Awesome! I love mill!

Hi there, had similar decks before so I might be able to help a bit.

* Portent is so much better than Eye Spy, why don't you max out the Portents?

* Ghoulcaller's Bell is an odd choice as your mill card. Is this due to budget contraints? I would at least upgrade this to Codex Shredder. The problem with the Bell is that it always works on both you and the opponent, so when you want to mill one but not the other, you are stuck.

* I'd love to see a Conundrum Sphinx in this! It would add a bit of beef to the deck and the effect could be quite handsome in this.

* Since this is Legacy and you splash black already, have a look at:
- Lim-Dûl's Vault
- Sealed Fate (could replace the Cruel Fate)
- Diabolic Vision

* I love Spy Network, however, it's just overkill in this deck. At some point you'll know whats going on and what you really need will be some actual defense for things that slipped. The problem with this card is that it doesn't replace itself like Portent does - if you draw it when you already know what's on top, it's basically a wasted draw.

* Check out Wand of Denial. It's actually your entire deck compressed into a single card^^ Of course you won't be able to spend life forever, so you'd also need some lifegain.

* This may not apply to your metagame but generally, these days, it's very risky to mill opponents without any way to exile their graveyards! There are countless creatures that can come back from the grave on their own, there is flashback, delirium, retrace, dredge etc. and generally you just don't want to give your opponent more options for things like Eternal Witness. I would add Necrogen Spellbomb to solve this. The beauty of the spellbomb: If you use black mana to activate it, you'll draw a card. So, when you draw it but don't need to exile graveyards, you can activate it anyway to draw something else. It's like cycling. If creature animation is the only thing to worry about in your meta, you could use Crypt Incursion instead, which would also solve your life gaining problem.

* Even if you don't add any of the black cards I suggested you need to adjust your mana base and add more black sources or ways to fetch the ones you have. Yes, you have a lot of library manipulation to find it, but I'd run at least 4. Jwar Isle Refuge, more Temples, Dismal Backwater, there are many alternatives that don't cost much.

* You have tons of cards to look at the top pf library and some ways to mill offending cards. But I see zero cards that can handle anything that the opponnet manages to slip through (which will inevitably happen at some point, especially during the first couple of turns). I'd have something like Silumgar's Command as a backup plan.

So, to sum it up, I would do something like this:
- 1 Cruel Fate
+ 1 Sealed Fate
- 2 Spy Network
+2 Wand of Denial
- 3 Eye Spy
+ 1 Portent
+ 2 Necrogen Spellbomb/Crypt Incursion
- 4 Ghoulcaller's Bell
+ 3 Codex Shredder
+ 1 Silumgar's Command
- 2 Island
+ 2 Jwar Isle Refuge/Dismal Backwater/Temple of Deceit

Which still leaves no room for other suggestions I made like Conundrum Sphinx but meh :)