At one point I was looking at a 4 color (nono-red) build, but there were enough combos for my purpose in Abzan, and it made the mana much smoother. If I had to add blue, I'd probably change commanders to
Atraxa, Praetors' Voice, but that also makes you more of a target at the table than you really want to be. These combos were not included for one reason or another.
Stuffy Doll + Pariah/Gideon's Sacrifice: Enchant Stuffy Doll with Pariah, and if the Stuffy Doll chose you, any damage to you will draw the game. Left out because Gideon's Sacrifice + Sivvi's Valor is both cheaper and less suspicious to pull off.
Assault Suit/Jon Irenicus, Shattered One + Skeleton Ship/Lurebound Scarecrow: Similar to the other can't be sacrificed combos above, these ones are more suspicous cards to play, and/or add in blue as a 4th color. There's also like 20 other "sacrifice ~ when" creatures, but most are wildly unplayable (islandhome/foresthome) and thus suspicious inclusions.
Teysa, Orzhov Scion + Darkest Hour + Heartless Summoning: All of Teysa's spirits are black, so they always create a new spirit when they die to Heartless. Not included because Darkest Hour is a pretty suspicious card to include, and Teysa doesn't have a ton of white or black tokens in this deck to use otherwise. Also doesn't combo with Ascendant Evincar in play.
Bishop of Wings + Conspiracy/Arcane Adaptation + Heartless Summoning/Ascendant Evincar: All creatures are Angels, so any 1/1 (Spirit) Angels die to Heartless Summoning/Ascendant Evincar. Not included because Bishop never triggered otherwise without Conspiracy, so starting the combo still required another card. Also note that with blue all the Conspiracy combos (except for Requiem Angel/Wildwood Scourge) could use Arcane Adaptation as well.
Essence of Orthodoxy + Chatterfang, Squirrel General + Conspiracy/Arcane Adaptation: Essence of Orthodoxy will continue incubating as long as Chatterfang can create Phyrexian Squirrels. Not included becacuse there is no other real Phyrexian theme to the deck, so it looks like a pretty suspicious inclusion.
Mikaeus, the Unhallowed + Tatterkite + Heartless Summoning + Ascendant Evincar: Tatterkite can never get counters, so Mikaeus will bring it back even if it always has 0 toughness. Not included because you need both Heartless Summoning and Ascendant Evincar in play due to Mikaeus' anthem, because Tatterkite can't combo with Luminous Broodmoth, and becacuse Tatterkite is just an inherently suspicious card to play in a deck.
Wildwood Scourge + Spark Double + Conspiracy: Conspiracy making the non-Hydras able to see each other, and the fact that Spark Double can enter above 0 toughness means an ever growing pair of not-Hydras. Left out because of requiring blue. Also can work with any other of the million blue clones, but requires Mikaeus (or another anthem) to not let the clone die as a 0/0 on ETB as well as a way to put a +1/+1 counter on one of them.
Tireless Provisioner + Chatterfang, Squirrel General + Life and Limb + Arcane Adaptation : Play a land to make a token, which makes a Squirrel Saproling Forest. Same as the included combo with Conspiracy, but left out because of blue.
Blowfly Infestation + Nest of Scarabs: A little hard to set up, but if you have 2 1/1 creatures in play and a way to make one die with a -1/-1 counter on it (say via Yawgmoth, Thran Physician, though you'd also need a way to get rid of him to combo), the second 1/1 will get targeted by the -1/-1 counter from Blowfly Infestation, and Nest of Scarabs will complete the combo from there. You need 2 creatures to start the combo usually because you always have to have a creature in play for the -1/-1 counter to target at the time you put both the token creation and -1/-1 counter triggers on the stack. You also need to have no other creatures in play to target to make this a mandatory loop, which is unlikely to happen. Not included because it's so fiddly and unlikely to combo off, as well as being pretty useless cards on their own.
Renegade Rallier + Animate Dead + Heartless Summoning + Ascendant Evincar: With revolt active and Renegade Rallier in the graveyard and Animate Dead in hand, cast Animate Dead to return Renegade Rallier. The two -1/-1 effects ensure Renegade Rallier dies, along with Animate Dead before the Rallier's triggers get put on the stack. Assuming there's no other targets for Renegade Rallier's trigger or Animate Dead (not super likely), the game will be a draw. Not included because of how unlikely it is to have 0 other animate dead targets, along with requiring revolt to trigger beforehand and having to have Renegade Rallier in the graveyard to start.
Garruk Relentless
+ Spark Double/Clever Impersonator: Clone the Garruk and then fight something to try to transform the clone. The clone doesn't have a back face though, so it will continuously try to transform forever. Left out because of blue, but this one is pretty cool, and all the pieces are useful elsewhere.
Ranar the Ever-Watchful + Portcullis: With both in play, all the spirits Ranar creates get exiled to Portcullis, which triggers him again. Not included because of blue, and also Ranar is a little suspicious of an inclusion without more support.
Eloise, Nephalia Sleuth/Pitiless Plunderer + Titania's Song/March of the Machines: All of the clues/treasures have legs, but also 0 toughness. Luckily, we can always make more. Not included because of blue and because Titania's Song (ATQ)/March of the Machines (MRD) are pretty suspicious inclusions.
Caged Sun + March of the Machines/Karn, the Great Creator + Ashaya, Soul of the Wild: Caged Sun is a creature Forest, so if it's set to green, it sees it's own mana ability add green and tries to do the same forever. Notable for being a mana ability that draws the game, so nobody can even intervene to stop it. Left out becuase it is pretty expensive to pull off (it doesn't work with Titania's Song either). Animating artifacts also has pretty limited utility with only ~10 in the deck.
Caged Sun + March of the Machines/Karn, the Great Creator + Life and Limb + Conspiracy/Arcane Adaptation: Similar to above, but even more clunky.