This is a stupid, awful combo with way too many pieces to be even a little bit viable, but that's why we play Commander, right?
I don't know who at Wizards R&D is responsible for Nexus of Fate, but I do know that it was a mistake for a wide variety of reasons. The newest reason on that list is that it enables an infinite turns combo with Kaho, Minamo Historian. Now, Kaho's ability can be a wee bit confusing, so I'll try to lay it all out here as best I can:
Kaho Kahmplications
When Kaho enters the battlefield, you tutor three instants from your library into exile. You can then pay one of those instants' converted mana cost and tap Kaho to cast it from exile. Note that this isn't quite like something such as Isochron Scepter or Elite Arcanist, which copy their exiled spells and cast them; Kaho actually casts those specific cards you pulled from your deck, meaning they will leave exile and go into your graveyard. This makes Nexus of Fate a prime target for her, and thus making it the linchpin of this combo.
However, Kaho's ability comes with some complications. Due to the nature of ETB triggers, every time Kaho enters the field, she's considered a "new" creature. Therefore, any spells you exiled with previous Kaho triggers will be exiled and unusable if you don't cast them before she leaves play. This means you need to be absolutely sure that she will be safe when you target Nexus. To reiterate, never go shields-down when you plan on grabbing Nexus with Kaho, or it will be lost forever if she leaves play before you cast it.
The Kahmbo
With that out of the way, how do we actually pull this big dumb combo? For that, we require a number of pieces, including a handful of mana rocks (preferably things that generate two or more mana, such as Basalt Monolith and Sol Ring), Paradox Engine, and an Essence Flux attached to Isochron Scepter. You can probably see where this is going already, but I'll walk you through it anyway:
Paradox Engine untaps all nonland permanents you control whenever you cast a spell, so if you've got artifacts capable of generating three or more mana, you can generate infinite mana by flickering a creature with Essence Flux on Isochron Scepter. You float all your mana, activate Scepter, untap with Engine, float all your mana, flicker, untap, float, flicker, untap, etc. So whenever you flicker Kaho, you can pull three new instants out of your deck. The combo comes from being able to flicker her and cast Nexus either immediately or on an extra turn after having already cast it. Ideally, you should also have something that will enable her to use her ability the turn she is cast, thus the inclusion of Swiftfoot Boots, Lightning Greaves (both of which offer protection as well), and
thousand-year elixer
.
Once we've got our pieces on the field, it goes like this: you cast Nexus of Fate from wherever you can- hand, Kaho exile, whatever- you get an extra turn, and Nexus shuffles back into your deck. You then use Isochron Scepter to cast Essence Flux and flicker Kaho, which in turn untaps all your artifacts and lets you grab three more instants. Nexus of Fate must be one of the three picked; you want to keep taking turns before your opponents, right? Now, if you have something that gives her haste on the field, you can just cast Nexus again, flicker again, and do this as many times as you want to pile on those extra turns. Otherwise, you can just wait until next turn to do it, which also eliminates the need for Paradox Engine (as untapping all your mana rocks doesn't mean anything if you can't cast Kaho's spells right away).
Kahmplete Your Victory
As to actually winning the game, we've got a couple methods at our disposal. Docent of Perfection
/Final Iteration, Metallurgic Summonings, and Talrand, Sky Summoner give us creatures every time we cast an instant or sorcery, of which we are running quite a lot. Otherwise, we can use the infinite mana combo to draw out with Pull from Tomorrow or Blue Sun's Zenith and win with Laboratory Maniac.
Kahnclusion
As to the other cards in the deck, we're mostly running evasion, cantrips, and other types of control and trickery. Draw cards until you get your pieces, counter stuff to keep them alive, and just try to stay in the game until you win out of nowhere (or just smack them with flying wizards and a giant bug). Risky? Yes. Inconsistent? Of course. Stupid fun? Absolutely. This is obviously a very casual deck, but I would love to see a better player and brewer build something around a similar combo. Kaho, Minamo Historian is a card I've wanted to build around forever now, and it seems like there's finally something cool to do with her.
