People sight when I play this deck
THE CREATURES
Firstly, we need millers. Our very first creature is Ruin Crab, the beloved first drop. It's cheap, a decent early game blocker, and on the long run, can mill a LOT if left unchecked by the opponent. Next is Cruel Somnophage. This creature is great as the adventure effect mills a decent amount, and then you had a creature to that? Cherry on the cake if you ask me. Sure it's only creatures powering it up, but for a colorless and a black, worth it. Sewer Nemesis is our next miller, while definitely slower than the others, it makes the opponent extra cautious when playing spells, as it can turn against them since we benefit so much from graveyards. Nemesis of Reason can easily be a finisher, usually by the time you can cast it, you've milled the opponent for quite a bit, so adding an extra 10 cards in the graveyard can very well deal the finishing blow.
Phenax, God of Deception can turn all of our creatures into millers. It's very easy for this deck to have 25/25s on the board, so now you can just tap them to essentially double their power and toughness? And also mill them this much? Mama.
The rest is mostly utility or straight up big creatures. Thing in the Ice
is for some board control in case you're not lucky on the creature draw or if the opponent had some removal. You have plenty of spells to transform it fast. We do run a few non-horror creatures, but in the case of Ruin Crab and Cruel Somnophage it's ok and can even benefit us, as the former is only a one drop, and the latter can be used for its adventure again! Regarding Phenax, he won't always be a creature so it's ok too.
Zellix, Sanity Flayer is pretty strong as it can create a ridiculous board pretty fast, however he's not very vital to the deck, if needed he can be swapped out for something else. Especially seeing its price rising recently.
Finally, Captain N'ghathrod is insane. Allowing us to mill many cards, but also reviving a creature that died this turn for free? This will have your opponent think very hard on how to block, a useful tactic if you want to leave them with few braincells.
THE SPELLS
Mill, mill, mill, little bit of draw, little bit of counter. The counter spells are great since it can buy us time until we can cast our 5cmc creatures, but it does make our opponent hate us even more. The winner here is clearly Glimpse the Unthinkable. For the splendid cost of 2 mana your opponent mill 10 cards, that's a 6th of their deck! That gives us a 10/10 Consuming Aberration! It's great.
Now, having said all that, our opponent drops a Bojuka Bog. It is turn 8, our hand is almost empty, our board is full. Our big creatures are 0/0 and die. We lost.