This deck is a cEDH Dimir Consultation-type deck. Atris provides color identity and some card advantage, as well as a chance to interact with your opponents in a fun way. Atris (and other creatures in the deck) can be blinked for card advantage with Thassa, Deep-Dwelling. Typical cEDH mana rocks, including Thought Vessel (and Reliquary Tower) to allow you to keep all the cards "drawn" with Necropotence and/or Ad Nauseam. The deck runs a good number of tutors and tutoring effects for between 1-3 mana (it is an Oracle deck, after all!). Shred Memory and Muddle the Mixture are decent instants on their own, but they are usually transmuted for other 2-drops in the deck. Spellseeker and Trinket Mage are more tutoring effects, often re-usable with blinking or reanimation effects. In addition to mana rocks, Trinket Mage finds other good 1-drops like Divining Top or Pithing Needle. Dark Petition is the most expensive tutor in the deck, but with spell mastery (easy to do) you get back BBB when it resolves--perfect for casting a Necropotence or Doomsday.
Okay, Doomsday piles. A five-card library upon resolution. A sold 5-card pile (in order) would be: Predict, Thassa's Oracle, Reanimate, Lotus Petal (or a free counterspell!), and Jace, Wielder of Mysteries (the backup win condition). If you control two islands you can use Gush instead of Predict in the 5-card Doomsday pile. In any case, you are winning with the Oracle's trigger and Jace as backup. For added redundancy the deck also runs the OG Laboratory Maniac.
Because there are three "I win if I have no library" type cards in the deck (Lab Man, Oracle, Jace), there are several other ways to exile your library that don't involve Doomsday. The most well-known is Demonic Consultation, but Divining Witch also works well as a backup plan. Consultation is faster, but one nice thing about the Witch is that it can be used twice, first to find Thassa's Oracle and then a second time to exile the rest of your library. Two other important library-exiling cards are Mirror of Fate and Thought Lash. Mirror can be used like Doomsday, provided you have another way to exile cards from your library first (like Thought Lash or Demonic Consultation). Copy Artifact on Mirror of Fate is also a better Doomsday effect.
Counterspells are pretty typical. Fierce Guardianship is replacing Negate, even though our Commander is a 2-toughness 4-drop. The thing is, most of the time your opponents won't focus on killing Atris on board because it's non-threatening and will only provide you with more card advantage if it returns to the Command zone. I often make a big deal talking about how much I want my opponents to kill my Atris (and they don't).
Card advantage in Rhystic Study & Mystic Remora and some blue cantrips. Gitaxian Probe is good at looking at an opponent's hand to see if they can stop you from winning this turn, and Telepathy is there for the same reason (and although the card disadvantage for you is slight, the annoyance factor Telepathy creates for some opponents is mighty!) Cephalid Coliseum is good for loot-three or forcing your opponents to loot-three (if they are also a Thassa's Oracle deck, for example). Snapcaster and Jace, VP are useful for recasting the many instants and sorceries and provide card advantage, as does Baleful Strix. The bird is the word--a cantripping, 1/1 deathtouch flying artifact 2-drop.
For creature removal: Cyclonic Rift, Black Sun's Zenith, and Go for the Throat (all two-drops!) and Toxic Deluge. Animate Dead and Reanimate are useful for getting your dead creatures into play and can be used on your opponent's stuff to further annoy them (along with Bribery and Praetor's Grasp). Tezzeret the Seeker is 5 mana but does amazing things tutoring up artifacts like Mana Crypt, Baleful Strix, Senesei's Divining Top, etx.
This deck does not run Tainted Pact because I wanted a more consistent U/B mana base and I chose to run quite a few basic islands and basic swamps. Not running Tainted Pact with all non-basics is arguably a mistake, but running 17 basic lands allows me to also run Back to Basics. Which can really shut down decks with non-basic mana bases. There are a few fetch lands to thin the deck, as well as about 10 other non-basic lands that mostly provide U/B mana. Ancient Tomb is a little bit of colorless ramp and Gemstone Caverns if you're feeling lucky about what the Oracle told you.
That's it, Oracle combo.
