Hello,
This deck is built around the combo with Arcane Adaptation + Chamber Sentry + Liliana, Untouched By Death + Diligent Excavator that I found out from this video by MegaMogwai: Liliana Historic Mill | Ravnica Allegiance Standard Deck (MTG Arena), which he modified from a version he found on MtgGoldFish called: Instant Deck Tech: Grixis Historic Mill (Standard)
The idea is to make everything into a zombie so that you can cast Chamber Sentry from the grave for 0 infinitely via Liliana, Untouched By Death's -3 and trigger Diligent Excavator until you mill out your opponent.
I found those version a little bit too janky and all in on the combo, so I made my version mostly black with a splash of blue in a way that would allow you to play the Death Baron along with a bunch of skeletons that can be brought back from the grave to trigger the Desecrated Tomb so you can have a decent presence on the board instead of just praying you get the combo pieces you need while you hold back. Desecrated Tomb sort of replaces Diligent Excavator for me. Infinite bats ftw! I only have 1 copy of the Diligent Excavator in the sideboard (which I can access with Mastermind's Acquisition) if it happens to be the only missing piece, because otherwise it's pretty useless outside of the combo itself. I also have 1 of each combo pieces in the sideboard to keep them safe from an Unmoored Ego, just in case.
Once Arcane Adaptation is on the board and makes everything a zombie, some fun interactions can happen:
-Every bat is a zombie, so they can get +1+1 death touch from the Death Baron.
-Chamber Sentry can also get death touch so using 1 of its counters to deal 1 damage to a creature is lethal.
-Liliana, Untouched By Death's +1 is much easier to hit.
If you already have 1 Arcane Adaptation in play, you can still play another to make everything into Demons to eventually trigger the 1 Liliana's Contract in the deck. It's pretty easy to have 4 different creatures in play since Gutterbones and Reassembling Skeleton keep coming back, usually with bats. Also, it's super flavorful since Lily's in the deck!
(I like to think my 2 Vraska's Contempt sort of offset the 4 life loss from Liliana's Contract.)
Priest of Forgotten Gods can be pretty hilarious too if you have a Desecrated Tomb in play, you could trigger all 4 Priests with just 2 mana and a Reassembling Skeleton in the grave.
Chemister's Insight can be useful to put the skeleton in the grave via jump start.
You do have to be careful not to screw yourself on the combo by still having a Death Baron on the board when you try to go off because he would prevent the Chamber Sentry from dying, that's why keeping some Vicious Offering in hand can be a good idea.
The sideboard is mostly all about having extra combo pieces, wipe the boards, and Blink of an Eye to get around cards such as Ixalan's Binding.
Thanks.
Dan.
