Obviously I like the deck, but a few comment's/suggestions.
How often do you have a character for Pulled Under? Doesn't seem like you have enough targets that can use the card reliably.
I definately don't think you need Dimensional Rift. By the time you can play this card I imagine you should ready be in control. This is unless of course that your meta is filled with control or other decks similiar to you own. Then by all means.
Likewise for Ravager of the Deep. While he is certain to put your opponent on his heals for a moment, you're definately too control heavy to need such a card.
Also, not a fan of Sacrifical Offerings here either now that I think about it.
Ideally you never want to a step back as you want to continually be pressing your opponent as you remove every bit of hope that they can muster. Sometimes you can't help that obviously, but that should be your goal.
If you do remove those, that would give you 6 slots to fill. 2 should probably go to snow graves. Discard pile tricks completely undermine what your trying to do so its usually best to not let this happen. Another card I thoroughly enjoy is a couple copies The Terror of the Tides. Since you can play it on your opponents turn it can be just as good as removal and provides a little beef to your deck. Also doubles as a good pitch card for Magnus.
2 open spots left... I think I'm gonna suggest the Temple of Ry'leh. Its not out yet, but can be amazing if you need the extra kill. Other decent options are Opening the Limbo Gate to combo with your Terror of the Tides, Ancient Ones or anything with a CIP ability. Speak with the Dead wouldn't be bad either for digging and recovery. There are several fun cards you can use for those two remaing slots or feel free to re-slot my suggested take-outs. They're not bad choices, but felt that they hurt your offensive pressure more than helped.
Hope you found that useful and good luck.