Here are my thoughts regarding March of the Machine, March of the Machine: Commander, and March of the Machine: Aftermath. I am also potentially including cards from Warhammer 40k Commander since I got behind a little:
Faerie Mastermind - Cloning this can easily break the symmetry of giving everyone a card with the ability. I don't know how much I need it here but it seems like one of the more powerful cards in the set that I might try it anyway. This is one of two decks where I think it might not be needed though.
See Double - Another Instant timing Clone is great and one that also has some versitility is even better. I am sure I can find some room for this as it fits the theme of the deck perfectly and looks to be a pretty powerful card in the right circumstances.
Vesuvan Drifter - This is an interesting card, especially in the context of the more recent discussion with trying to get more attack triggers. The main question is whether there are enough creatures worth copying and I believe the answer is no. For all the
Pathbreaker Ibex and
Elder Gargorath that I could copy, there are a lot of clones and things with ETB triggers. So, I don't think this is quite the card for this deck.
Necron Deathmark - Another good creature to clone and having Flash allows for a few different options. Flashing it in when needed and then cloning it on my turn helps clear up some of the board. 5 mana is tough to do but I think it is worth it to get some additional destroy effects.
Invasion of Ikoria - This looks to be a better
Green Sun's Zenith. Sure, it costs 1 more mana but can also grab things out of the graveyard and is not limited by color. It can't find Humans but that is not that big a deal. And the back side is pretty powerful if it sticks around and can just win games. If nothing else, I think a straight swap makes sense but I could also see finding room to add this to the tutor suite.
Callidus Assassin - This just looks like a cool creature. 6 mana is a lot but a Flash clone and a potential ETB destroy effect is nice in one package. I don't know where it would go but it seems good for the deck.
Zimone and Dina - This looks pretty powerful. I don't think I have a lot of traditional sac fodder but there are likely things that make sense to sac to not only get the effect here, but to then reanimate or clone to get more ETB triggers. And they fit into the curve pretty well at 3 that I think it makes sense to try out.