Atemsis, All-Seeing: Creature that supports exactly what the deck wants to do. Decently sized flying body that offers card advantage and immediate clock, fueled by the deck's main focus.
Archaeomancer: all-star that gets back any of the juicy instant or sorceries that the deck runs.
The philosophy of this deck is to keep moving forward, not relying on past spells too heavily in order to win. As such, this creature is the only form of direct instant/sorcery recursion in the deck. Use it wisely.
Azami, Lady of Scrolls: While she may seem out of place in this deck, there are a couple of wizards in here that turn Azami into a lethal weapon. The UUU devotion is appreciated along with the consistent card advantage. This slot is a bit flexible right now, but I am rarely unhappy to see her.
Cavalier of Gales: a 5/5 flyer for 2UUU that brainstorms on ETB then shuffles + scrys on death. While the deck does not offer a lot of search to take advantage of the brainstorm alone, it definitely loves the body and the UUU devotion. Anything that puts cards into the pilot's hand while also offering upside is worth a slot to me.
Consecrated Sphinx: Do I need to explain this guy? He wins the game on his own. If he somehow tables, Sakashima him and enjoy the fun.
Dazzling Sphinx: This card can be hit or miss, the but the risk is not worth letting this stick. I consider it a must answer 5 drop. Card advantage that cannot miss as a reward for attacking, right up this deck's alley.
Gadwick the Wizened: Blue sun's zenith stapled to a body, yes please. His second ability is relevant to tap down blockers, letting this deck's creatures get into the red zone. Solid card all around.
Gilded Drake: The creature theft in the deck. An indefinite steal for ? Yes please. Works disgustingly well with Sakashima since he can clone the exchanged guilded drake to steal something else.
Inspired Sphinx: Effecttively another copy of Sphinx of Uthuun. Solid body, card advantage, and a mana sink all in one.
Kozilek, butcher of truth: One of the OG titans himself. He tops out the mana curve as a serious threat, while also drawing 4 cards. If he gets removed, big deal. You just drew 4 cards. The annihilator means that he will wreck players that cannot remove him from the board. Additionally, the graveyard shuffle effect helps protect the deck from milling. Of course, he is an excellent body for Sakashima too.
Kozilek can be used with Nezahal manually shuffle your GY back in by discarding him to Nezahal’s ability. Keep this in mind if you are in a danger to a windfall effect.
A word of caution with Kozilek: Try to avoid casting him when there is mana up for a theft spell (3 or more), or if you cannot protect him from a red theft spell and cannot handle sacrificing 4 permanents. Eldrazi turned against you are devastating, so make sure you are ready to play with fire. If kozilek gets stolen directly out of your deck, try to have sakashima at the least as a bargaining chip to dissuade early annihilator wars.
Master of Winds: Another medium sized sphinx that loots. Solid body that can hold the fort or be a decent attacker as you continue to cast spells.
Nezahal, Primal Tide: this dino is a powerhouse. It draws cards for any non creature spells, gives you no maximum hand size, can protect itself, and can’t be countered. All on a 7/7 body. Nezahal can win games by itself, especially if you get two via sakashima. If you use the blink ability for both of them at the same time, make sure to stack your triggers so that Nezehal comes back first. Then, Sakashima can copy it again.
Phyrexian Metamorph: This guy is the 2nd and last clone effect in the deck since Sakashima handles that job pretty well himself. The bonus here is that the metamorph costs 2U and 2 life if need be, and it can copy artifacts. This versatility earns it a spot in the deck even though Sakashima is a clone.
Sakashima the Impostor: One Sakashima is not enough, clearly. This one can clone enemy creatures and return himself to your hand. Very abuseable.
Scourge of Fleets: This thing is great in a mono deck because your island count is likely to be high. This often translates into a one sided creature wipe, and a repeatable one at that since Sakashima is in the zone. Other than that, a 6/6 is no joke.
Solemn Simulacrum: Sakashima can reuse the body, otherwise it ramps and draws cards. This slot is a bit flexible and may be changed to Urza, but Solemn seems fine so far.
Sphinx of Foresight: this guy is a solid 4/4 flyer for 2UU and has an amazing pregame effect. Late game, it helps you dig deeper into your library for gas by bottoming dead cards. Solid card all around.
Sphinx of Uthuun: 5/6 flyer that gives you fact or fiction on a body. Value all the way and can be sakashima’d for further use.
Tidespout Tyrant: this guy is a tyrant indeed, as he can reset the board quite fast. At the least, he tacks boomerang onto any spell you cast. At the best, he combos with Sakashima, mana crypt/sol ring, and a 2 cmc or less rock to bounce everything you do not control. The game usually ends once he drops.
Trinket Mage: this guy is versatility incarnate. With the solid artifacts this deck is running, there is always a relevant target. For early game ramp, go get mana crypt, sol ring, or wayfarer’s bauble if you are worried about artifact removal. Mid game to late game, go for expedition map in order to dig for a more relevant land, or a combo piece with tidespout tyrant.
I usually like including an artifact land when running this guy in order to make sure he can always tutor out a land drop if necessary. That is not necessary with the card draw options in the deck and access to mana crypt.
Ulamog, the ceaseless hunger: Kozilek’s buddy also tops out the mana curve at 10. He will get you out of virtually any situation with his exile cast trigger, and he will end the game in a couple of turns with a few unchecked swings with his exile mill trigger. He is super helpful for the deck even if he does not stick just for the fact that he can exile any permanent, some of which struggles to deal with.
A word of caution with ulamog: be careful about tapping out to cast him. He is devastating when he’s coming at you, so try to hold up some kind of answer to red theft, blue theft + haste engine, or spells like aethersnatch or desertion (so and 3+ up). Black, white, and green can’t turn a resolved ulamog against you easily, so don’t worry about them. On the flip side, be careful about discarding him with black at the table unless you can hold up countermagic for a reanimation spell. If you cannot do this, keep sakashima in the zone so that you can get a ulamog too if he gets reanimated. Bargain with the thief to not get into an early eldrazi war, as it’ll make both of you extremely unlikely to win the game.
Unesh, Criosphinx Sovereign: If you have read to this point, you’ve probably noticed there are a lot of sphinxes in this deck. Aside from being good creatures, this guy is the other reason there are so many. Unesh is the real lieutenant of this deck, and him resolving and tabling will likely result in your victory. The mini (read: 1 card less) fact or fiction for his ETB or any sphinx etb’ing is insane card advantage, but there’s more: he ramps sphinx spells. When you have two of him? It almost isn’t fair. Unesh should eat removal immediately, but have a field day if he sticks.
Urza, Lord High Artificer: Ramps, makes a large body, and sinks mana for value. Makes Malcolm's treasures into permanent mana rocks, worth a slot.