I activate Reasoning and when my opponent has no response, I chain with Serial Spell. My opponent guesses Lv1 for both Reasoning effects. Assuming Sacred Crane and DMoC are the next two monsters in my deck, what would happen?

Would I special summon both thru Serial Spell and Reasoning, then resolve their effects in a chain, gaining a spell back for DMoC and drawing a card with Crane (or the other way around, someone clarify plz)

OR

Would I special summon Sacred Crane for Serial Spell's effect, draw a card, and then resolve Reasoning and summon DMoC to regain a spell?

I think you would have to resolve one of the Reasonings effects before the other.

Also, if Sacred Crane was the first monster summoned and then DMoC, I think that the effect of Sacred Crane would have to wait for the current chain to finish resolving, before your able to draw a card. I'm not sure whether you chain the effect of DMoC and the effect of Sacred Crane, so that DMoC's effect comes last and you don't miss the timing (if it is a case of that). Thats what I think, but I'm not too sure myself.

Chains resolve backwards, so it resolves like this:

Reasoning #2 (the serial spell):
Reveal top card - it's a Sacred Crane, so it gets special summoned. Sacred Crane's effect is mandatory, not optional, so it will form a new chain at the end of the current chain.

Reasoning #1 resolves (the original one):
DMOC is the next card, so he gets special summoned. His effect is optional, so you have to wait until the chain is over to activate it, and you can only activate it if his special summon is the last thing to occur or else you miss the timing.

The chain is now over and DMOC's special summon is the last thing to have resolved, so you are permitted to activate his effect. Since Sacred Crane's effect is mandatory, its effect automatically goes on chain link 1. DMOC's effect will go on chain link 2.

Assuming you have no other effects to put on the chain, it will resolve backwards. First you will retrieve a spell card from your graveyard, and then you will draw a card from your deck.

I hope that did not confuse you.

Remember that these effects will never interrupt an already-resolving chain. Mandatory effects automatically take up chain link 1, and then the optional effects, if the timing is not missed, will go on the chain after.

Sacred Crane's effect would Trigger, but cannot resolve in a resolving chain, and would have to wait until the Chains complete resolution. If DMoC is the first monster summoned, since his effect is optional, you would miss the timing.

Chain Link 1: Reasoning
Chain Link 2: Serial Spell

Resolution:

Chain Link 2: Serial Spell -> discard all hand to the graveyard, opponent declares a level (in this case lv 1), pick up cards from deck, summon Sacred Crane. (wait for the chain to end for drawing a card).

Chain Link 1: Reasoning -> opponent declares level (in this case lv 1), pick up cards from deck, summon DMoC (select Spell Card).


EDIT: My bad I thought Serial Spell was for Sacred Crane and Reasoning for DMoC.

Sacred Crane's effect of drawing a card has missed timing (it can't be activated).

Dark Magician of Chaos' effect would only resolve IF you don't discard any cards at the conclusion of Reasoning's effect (Chain Link 1).

Both of your statements are incorrect.

The first one: The effect of "Sacred Crane" is a mandatory Trigger Effect, and cannot miss the timing.

The second one: Picked up cards from "Reasoning" being sent to the Graveyard will not cause "Dark Magician of Chaos" to miss its timing.