By combining two Mirror Images with a Cavalier of Night, you get infinite "destroy target creature" effects together with infinite enters-the-battlefield and death triggers. On top of the one-sided board wipe provided by this combination of cards, this deck also abuses the infinite ETB triggers with Risen Reef to put every remaining land card in its library onto the battlefield tapped and every remaining non-land card in its library into its pilot's hand for infinite turns with a one-of Nexus of Fate (which gets discarded to handsize and reshuffled into its one-card library at end of turn if it doesn't have enough mana to cast it the turn it goes off). This combo is made more consistent/achievable with both Fauna Shaman and Neoform, each of which can tutor for the missing pieces of the combo and put a Mirror Image in the graveyard to speed up the combo.

Edit: The deck previously also ran Ayara to abuse the infinite death triggers for infinite life drain, but I found it much clunkier than comboing off with Risen Reef. Since cutting her, there have only been a couple games where I wished I could've tutored for her instead of a Reef/Mirror Image, but in the end it rarely would've changed the outcome of the game. Maybe she'd make sense as a sideboard card against especially distruptive decks for an alternate win-con (against the likes of Unmoored Ego) and Nexus of Fate decks (which can kill you even after comboing off as you're unable to cast your own Nexus until after their next x turns in a row), though Unmoored Ego seems like the preferable card in the Nexus matchup and the deck has proven surprisingly resilient against Unmoored Ego as it's still very capable of decking itself without Cavalier of Night and beating down without Nexus or Risen Reef. Just wanted to make anyone interested in this deck aware of having the option to use her (and Overgrowth Elemental, for that matter).

Sideboard Plan:

Against aggressive decks, Disfigure and Massacre Girl of course come in. I cut Muldrotha and Blood for Bones in their place. You're unlikely to combo off against burn too, so it may be correct to cut all Mirror Images (which usually have no creatures to copy when they're all burned away) and replace them with Shifting Ceratops, though I haven't encountered it enough to know what is actually correct. Reclamation sage can protect you from Experimental Frenzy, too (no need for the expensive Nexus if you cut the Mirror Images). The key to winning these matchups is often just disrupting your opponent's board and finding and casting a Cavalier of Night as fast as possible to stabilize and then get ahead and beat down from there.

Against midrange decks, not much needs to change, though Gruul aggro is a tough matchup. I bring in Disfigures for mana dorks and Massacre Girl if they run the likes of Rekindling Phoenix. I'll often just cut 1 each of Neoform and Mirror Image together with a Fblthp if all three sideboard cards come in. Comboing off is less of a concern against slower creature-based decks with all the removal this deck runs. Focus on stabilizing first, then find the shortest path to the combo after (while beating down if you can). Though if you get off to a fast enough start you won't even need to stabilize.

Against control decks, bring in the three Hydroid Krasis and Tamiyo in place of the two Tyrant's Scorns and two Chupacabras. I know it seems strange to run Hydroid Krasis in the sideboard, but it doesn't belong in the maindeck with so little ramp. I tried. They often got stuck in my openning hand and I found myself wishing I actually had something useful in the early turns against the aggro and midrange decks I was facing. But against highly disruptive control decks that often make games go long without threatening your life total, Hydroid Krasis is the perfect top-deck after a board wipe or just to catch up with an opponent drawing too much gas. Tamiyo is similarly bad against agressive decks but strong against control, as she can recur whatever you may need from your graveyard and thins out your deck while she's at it. She doesn't fit well into the deck as she's not a creature and can't be neoformed into for cheap, but her passive abilities and long-term value make her worthwhile at least as a one-of. With these cards in your deck it's possible to outvalue even control decks and reach the infinite turns win-con even without combing off.

I will also always bring in Reclamation Sage to protect against the likes of Ixalan's Binding and give me an answer besides a one-of Assassin's Trophy to cards like Search for Azcanta and Phyrexian Arena (among others I can't think of right now). Lastly, if the matchup is against a very counterspell heavy deck (Simic and Izzet Flash obviously included), I will bring in the four Shifting Ceratops. Expensive, sorcery-speed cards like Muldrotha and Blood For Bones can be cut to make way for the dinos, together with one each of Neoform and Mirror Image. Casting spells that sacrifice creatures as part of their casting cost is painful when they're countered, and when games go long you can get away with having fewer than four Mirror Images to combo off reliably.

Lastly, against combo decks like Kethis and Nexus of Fate, Loaming Shaman, and both Umoored Egos come in. Umoored Ego is the perfect answer to any combo deck, with the decks' namesakes being the obvious primary targets of the card. Loaming Shaman comes in to shuffle opponents' graveyards back into their libraries, increasing the odds that a Nexus player will fizzle and preventing a Kethis player from comboing off early (as an added bonus, the shaman also protects against reanimator and mill decks). Reclamation Sage obviously comes in against Nexus players, too. Cuts are tough against Kethis. I've just been cutting one each of Fblthp, Neoform, and Mirror Image. Against Nexus, I cut the Scorns and the Chupacabras. Nexus is a very difficult matchup, with Unmoored Ego seemingly being this deck's only real answer to it.