Mill is great. We’ve said it before, we’ll say it again, and we’ll never stop believing because that’s clearly what Journey was singing about. We assume so, there’s no legal way to find the lyrics online, so nobody can prove us wrong.
While we’re on the topic of mill, it’s probably a great time to point out that we just got one of the most intense mill commanders we’ve had in ages. Plus, they even serve not one, but two different tribes. Let’s chat about Umbris.
You probably should fear Umbris

Umbris, Fear Manifest

Whenever Umbris or another Nightmare or Horror you control enters, target opponent exiles cards from the top of their library until they exile a land card.
, is a five-mana blue and black 1/1 that gets +1/+1 for each card your opponents own in exile. That’s an absurd ability, this isn’t counters, it’s just a flat buff. Sheesh. That’s not all though, they also read, “Whenever Umbris or another Nightmare or Horror enters the battlefield under your control, target opponent exiles cards from the top of their library until they exile a land card.”
On average, you’re only going to get around three cards per creature this way, but that still means that Umbris comes in as a 4/4 the first time around, assuming you’ve not exiled anything else, and then just continues to grow from there. That’s ridiculous just from a power front, and it’s absurd to have another one of these cards that grows so incredibly monstrous so quickly.
That’s not all though. Umbris caring about both Nightmares and Horrors means we can stuff this deck with incredible cards that don’t normally have a tribal home. It also means we can beat the ever-living library out of our opponents just for casting these horrifying creatures. We’re here for it.
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Is this just a night terror?

There are a lot of good Horrors and Nightmares you can include in this deck to just make it a fun tribal deck, but not as many if you’re looking at just mill. You do have
Nemesis of Reason

The main one that you’re going to want here though, is
Consuming Aberration

Whenever you cast a spell, each opponent reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.
, another five-mana Horror that reads, “Consuming Aberration’s power and toughness are each equal to the number of cards in your opponents’ graveyards. Whenever you cast a spell, each opponent reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.”
You can also branch out a little to include some Eldrazi, if you want to, with the main draw here probably being the likes of
Sire of Stagnation

Whenever a land an opponent controls enters, that player exiles the top two cards of their library and you draw two cards.
and
Oblivion Sower

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