OK, here goes. (Warning: the code is complicated and largely uncommented, and it’s very possible that I’ve misunderstood some of it.)

Activating a pact (1) incurs an immediate 0.5 units of “necrocorn deficit” and (2) incurs a further 0.0005 units of “necrocorn deficit” per day until the end of time.

By default, this doesn’t touch your actual stock of necrocorns. But a nonzero “necrocorn deficit” makes your pacts slightly less effective, in proportion to the deficit; and if the deficit reaches 50 units then Bad Things happen.

You can repay your debt, at a rate of 1 necrocorn per unit of necrocorn deficit, rounded up to the next integer number of necrocorns, by clicking the “Pay the debt” button. You can only do this when you can afford to pay your entire deficit.

If you haven’t taken the Siphoning policy, that’s it and you can stop reading here. Otherwise, read on.

First of all, siphoning doesn’t change anything about that initial 0.5 units of deficit per pact. What it does do is to try to pay off the ongoing 0.0005 units per pact per day automatically.

Good news: It does this incrementally and without rounding up to an integer number of necrocorns; as long as it’s able to keep up, it will keep your necrocorn deficit at zero and so the deficit will not decrease the effectiveness of your pacts.

Bad news: you pay a little bit more, in two ways which I’ll describe in a moment.

So, with siphoning, instead of the ongoing debt gradually building up your “necrocorn deficit”, there’s a three-layer thing. (1) So far as possible, the ongoing debt is taken out of your necrocorn production. Actual necrocorn corruption occurs discretely – an alicorn is corrupted gradually, bit by bit, until it reaches 100% corruption and abruptly turns into a necrocorn. But the siphoning process can use 1% of alicorn corruption to pay of 0.01 units of necrocorn deficit. (2) If pact-consumption is faster than marker-corruption, so that #1 can’t keep up, the consumption is repaid incrementally out of your stock of necrocorns – but you pay an extra tax for this. (3) If #1 can’t keep up and #2 runs out of necrocorns, then you accumulate necrocorn deficit just as you would have done without siphoning.

The extra tax defaults to 15%. That is, any time your pacts are consuming necrocorns faster than your markers are corrupting alicorns, your stock of necrocorns goes down, incrementally, 15% faster than the necrocorn deficit would have been going up without siphoning.

Some kinds of pacts make the tax higher or lower, always in proportion to the number of Black Pyramids you have. This is the “Necrocorn deficit recovery per pyramid” thing shown in the description of the pacts. So, e.g., the description of the Pact of Cleansing says “Necrocorn deficit recovery per pyramid: 0.3%”. This means that for each PoC you have, the 15% figure is increased by 0.3% for each Black Pyramid. So 25 BPs and 4 PoCs would mean an increase of 30%, turning 15% into 19.5%.

… Except that what the code actually does is more complicated than that, and I haven’t got my head around exactly what it does and why. (It looks wrong to me, but probably the confusion is all mine.) So the above is a Lie. My probably-inaccurate understanding of the Truth is below, but it’s complicated and (again) probably wrong. Read on at your peril.

Say that your “surplus necrocorn consumption” is the consumption of your pacts minus the amount you’re able to pay for from ongoing corruption. (So if this is <= 0 then everything’s fine, your stock of necrocorns doesn’t need to be touched, and there’s no tax to pay.)

Say that your “fully modified tax rate” is the thing described above (which is 19.5% with 25BP and 4PoC) and your “half-modified tax rate” is what you get if you do the same calculation but halve the change produced by your pacts, so that with 25BP and 4PoC it would be 17.25%.

Say that the “amount of tax” is the tax rate times the surplus necrocorn consumption.

If repaying your surplus necrocorn consumption while applying the half-modified tax rate would completely exhaust your stock of necrocorns, then add the surplus necrocorn consumption to your necrocorn deficit. (Untaxed – the tax is only paid when auto-paying ongoing deficit from necrocorn stock.) Then reduce your stock of necrocorns by the surplus necrocorn consumption plus the amount of unmodified tax.

Otherwise, reduce your necrocorn deficit by the amount of fully-modified tax, and reduce your stock of necrocorns by the surplus necrocorn consumption plus the amount of half-modified tax.

OK, so much for the tax and the “deficit recovery per pyramid”. I said, about 100 pages of text ago, that using siphoning imposes two costs on you for the convenience and the incremental-ness. One of them is the tax when you have to draw on your necrocorn reserves rather than just leaching off the corruption process. The other is a cost of leaching off the corruption process: whatever quantity of alicorn-corruption you use to repay your pacts’ ongoing cost, you also pay the same quantity of uncorrupted alicorns. So if you have 8 pacts costing a total of 0.004 necrocorns per day, siphoning will reduce your necrocorn corruption rate by 0.004 per day (as described above) and also consume 0.004 uncorrupted alicorns per day. Usually this cost is utterly negligible compared with your rate of alicorn production.

The only other thing I should say is a reminder that your rate of necrocorn corruption isn’t necessarily constant: it’s higher when you have no necrocorns. So if the rate of pact-induced consumption is faster than your rate of necrocorn corruption with necrocorns, then eventually you’ll consume all your necrocorns (with the weirdly-modified tax, as described above!), and then your rate of necrocorn corruption will suddenly increase. That may make it enough that you no longer need to try to consume necrocorns … until the quantity of corruption reaches 1 and you make a new necrocorn, at which point the corruption rate goes down again and you start consuming your newly-made necrocorn. All this happens with a granularity of one day, so if e.g. you have leviathans to feed and you’re quick about it you can feed that necrocorn to the Elders before it starts getting eaten bit-by-bit by the siphoning machinery…