Notes & Combos
The point of the build was to turn what usually are bricks (Harp and Knightmare) into high quality extension tools that let you play unfazed through interruption by being readily discarded. This conversion also opens a bunch of space up in the decklist, which allows me to play 17 NON-ENGINE CARDS.
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Stats I wrote code to calculate π: (In parantheses: with Crossout)
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Hands that play through Maxx "C":γ 43,7%γ(49,6%)
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βHands that play through Ash:γγγ52,7%γ(57,7%)
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βHands that play through Imperm: γ 44%γβ β β (50,1%)
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βHands that play through Veiler:γ γ55,5%γ(60,1%)
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Improvised how-to-play guide:
https://www.duelingbook.com/replay?id=4304-44631383
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Other notes:
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I chose Enemy Controller as my 16th and 17th non-engine because it was a Skill Drain out (CL1 Ding, CL2 Controller tribute Ding target Eldlich) that was also a useful (often even strong) card in every matchup going both 1st & 2nd.
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The deck opens Orcust combo 85,7% of the time going first and 91% going second (not counting "crash Harp into an opponent's monster"). So you will open hands that do not have immediate Orcust combo about 1 in 9 games.

I appreciate all the work you put into this. I've been wanting to play Orcust for a while and I think I'm going to build this, or something very similar. Typical end board is Union Carrier, IP, and Ding? Then go into Apollo and bring Ding back out turn 2? Also, what's the plan if Maxx C resolves first turn?

The plan vs Maxx C is that you play 17 standalone trap cards (5 of which completely counter Maxx C); Imperm Imperm Veiler is 3 negates through any handtrap!
That, paired with how most of your play starters can stop at the first Special Summon and still put Orcust cards in circulation for your next turn, makes getting Maxx Ced pretty fine.
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This is all in the duelingbook replay (https://www.duelingbook.com/replay?id=4304-44631383), but:
The standard, minimal board is IP Babel Carrier (Ding Harp Knightmare in GY), which gets you a 2400 ATK apo + Ding send and Wand followup, or 1600 ATK apo + Linkuriboh (Harp into Brass, then Linkuriboh revive itself) and Skeleton followup if they Lightning Storm/Duster the Babel.
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Any additional extension makes it so you can afford to keep the Ding on board instead of linking it off, which lets you play around Lightning Storm completely (you can keep it on field until they commit a face-up card to the field, at which point you can IP link it off into Apollo to set up the Skel Ding interruption) and also get an extra 800 ATK on Apollo (in that case, you will usually need to Harp special Girsu and send Skel off Girsu instead of directly getting to Skel because you wanna use Skel early on the Girsu you link off so Ding can absorb it).
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There is also an 8% hand where you open striker engine, sacred engine AND orcust engine, and that can produce the somewhat stronger board of 3200 ATK Apollo, Gala Crescendo, Linkuriboh.