Yata

@Velvet Thunder Many of the spoiler part isn't real Spoiler for this subforum, anyway: We don't know how a dead Shardblade looks if you see it from the CR but I assume you could not carry a Blade into the Cognitive Realm (not sure fact, only speculation) as the Blade itself is something possible only because the Spren is deeply dragged into the Physical. There are ways of harming Cognitive Entities, one if hurting their Soul (for example a Shardblade or some Magic Systems could be fine for this) the other is hurting/destroying their minds (in this case we know really less ways to performe this, for example Nightblood is one of them or...the Oathbreak is another). Radiant Spren are alive and sapient before they jump into the Physical Realm. In the physical Realm they need a Bond to mantain their sapience but they are still alive and sentient. When you broke the Oaths you damage the Spren's Mind (to be more accurate you rip away a piece of his mind). What I believe you don't understand is what the Spren call "death". It's not like our concept of Death, the Spren's Concept of Death is quite "have the Mind destroyed", The DeadBlades are not stricly dead...Simply "comatose" (it's a bit of strench but I assume you could understand better the metaphor in this way) after losing a great amount of their Minds. You could see this as the Deadblade are still vaguely capable of feeling and by the fact that a former Radiant could restore a Radiant Spren's mind simply reSwearing the Oaths (therefore returning to the Spren the missing part) as you saw with Kal and Syl at WoR's ending (yeah by the way, Kaladin killed Syl there, She didn't pop up as Deadblade just because Kal didn't progressed enough with the Oaths to allow her to materializate as Blade yet). Returning to your actual question, the Spren has not multiple istance of himself. If he is broken, he is broken in physical and in the Cognitive. On Nightblood's topic, Nightblood is a manmade Splinter (Spren are Splinters, or to be more precise Spren is a local term for what the Cosmere aware people will call Splinter). Their creators managed to packed together enough Investiture and the right circumstances to craft for a bunch of Kinetic Investiture a Splinter. They indeed tried to create A shardblade with their magic, this task was inspired by Rosharan SprenBlade but has not a specific purpose rather the accademic one. Nightblood is actually a Shardblade, this is true becase Shardblade is a term used to refer to object with some kind of caratteristics. The Roshar SprenBlades and Honorblades are just two istances of Shardblade possible. But as Nightblood showed us, it's possible to craft similar item also with other Shardworlds' magics. About "killing Nightblood" I have to use spoiler tag as there are some specific element not related to SA:

Lift had to be' alive in Arc2. Brandon stated that the reason to write Edgedancer as Novellara was to show a bit of Lift's development because when She will be a Central character (in Arc2), She would be far ahead as KR

The Cognitive Shadow stuff is something related to mortals (or three aspects beings) Upon Death. If they had enough Investiture infused their Soul...they could remain for a (arbitrary) while as some kind of poor Humanspren. CS and Splinters (Spren) are mainly the same thing with different origin and amount of Investiture. Asking for a Splinter's CS is almost like asking for a Cs' CS.

As Calderis said Adonalsium maybe had or not a Vessel. IF there was a Vessel, this Vessel Upon Death could choose to reach the Beyond. IF this Vessel choose to remain as Cognitive Shadow, the Shards could have destroyed him. IF the Vessel's CS was not hurted/destroyed. We don't know if he would be limited/trapped in Yolen as we don't know how Adonalsium worked at that time. A Cognitive Shadow is tied to places from the Investiture that compose him...as far as we know an Adonalsium's CS could be able to go everywhere there is a great amount of Investiture. PS: It's tangential but I saw you pointed on Leras. Leras/Fuzz was not a CS, he was a alive for the main part of Mistborn. He dies only in HoA and he didn't leave a CS

Nightblood is an artificial Splinter so he could die in the same way a Spren does...His mind could be destroyed or the Investiture that compose his being could be split apart/consumed

But Dominion was Splintered far before the Shu-Dereth's birth. D&D's Murder happened Almost in Sel's prehistory. A connection between the Vessels as cause is extremely unlikely.

I can't honestly say It is impossible but nothing point to a moving city. Urithuru is an huge structure and still bigger if you count the Oathgates' platforms....the simple fact that something so huge simply goes around Roshar unseen is extremely unlikely. Your point on Gravitation allows Szeth to detect Urithuru's location is quite ....a stretch, for example Kal didn't experience nothing strange with his Surge flying in Urithuru. I could understand you like the mobile-Urithuru idea, but simply you Need too much "assuming this" to be' considerate a likely option

The Royal Locks are genetic passed down from Vo's lineage but you express them only if you are in the direct line for the throne. For example when, one of Vivienna's sibling will inherit the throne, all the other siblings will lost the Royal Locks because they are no more in the direct line (in the same way an hipotetical Vivienna's uncle has not the Royal Locks also if he is the king's brother. Already explained because (to me) that happens and others disagree with my point...the fact remains, Vo's descendants on Nalthis gained and losed Royal Locks depending on their position regard the Idris' Throne

Maps never point where the city was because you could get there mainly by Oathgate and therefore nobody could preciselly figure where the city is....But it's in a fixed spot, you may see it from WoR's ending, where Szeth knows the exact Urithuru's location and it's ready to reach it when he understood Dalinar goes there. @Calderis I believe Jasnah Elsecalled back from Shadesmar, she had not Stormlight and therefore her first plan was to reach Honor's perpendicularity, but she could recovered a bit of Stormlight in her journey (maybe by the Spren)

Dalinar 's Memory Lost is caused by the Old Magic and by the way It's not a Simply Memory loss as every reference (past, present and future) is erased from his Active Mind. It's not related to Awakening

Ehm no... Bleeder uses a single Spike for Trell, She had not others Spikes in herself at the same time. Anyway you confuse what It's tradizionale and what is a rule. A Kandra Need two spikes to mantain his sapiency. But those Spike could any kind of Hemalurgic Spikes. in the Final Empire they uses only 4 kinds and always paired, but It's not a rule, they could make Kandra with different Spikes. Of course if you use a Blessing made of different metals, you Will not gain the same benefit of (for example) the Blessing of Potency. @Calderis except we saw directly in BoM they were unable to fix ReLuur unless they retrive his Spike...I think the WoB refer mainly to what Teenson does (use another Kandra's Blessing ad extra Spikes)

I know a Blessing is a couple of Spikes...but the spikes has not relationship to each other...they are not craft together or craft ti work together. About the original Blessing...Bleeder shows is that is not true as She change her Blessing with a new "half Blessing" and they change It multiple time in the book

Except they didn't work in that way. If that was the case the Kandra could Simply remove the other ReLuur's Spike to replace It with a complete pair.... Teenson tried to gave him his extra Spikes and didn't work. By the way, the Blessings aren't really paired...the Kandra Need only two Hemalurgic Spikes to stay fine, if they are of different metals or with different properties don't matter. They Just Need for the Spike to be' crafted from them (I believe It's more "nobody else used them")

Every Spike could be fine as extra Blessing but the "main ones" have to be crafted for them. It's the whole BoM's point...The Kandra can't Simply replace the Lost Spike with other they have avaliable.

The Blessing can't be re-used. It's the reason they could not increase their number. They are crafted and keyed to the first user

Marsh can't be a Splinter. A Splinter is sentient Investiture and Marsh is a mortal man (well an Inquisitor but still a mortal). Anyway, I am quite sure there is a WoB about the absence of Ruin or Preservation's Splinters

The problem remains, the Kandra are losing member and they could not make new one....Wayne could be turned into a mistwrath but without Blessings He can't become a Kandra

It's stated by a WoB that Kel's spike gives "nothing special"

No, you could not turn one kind of investiture into another...This is not really an issue as at their base Mists/Stormlight/Breath/Dor are all Kinetic Investiture and could be used for every magic systems...there are some hack to perform to do it, but it's possible (for example you could find a way to use Surgebinding fueled by Breath). The Selish magic is a special case as it's actually location dependant but as I said before, you could find a way to fuel magics with foreign investiture...Some are easy and others are not. By the way, you could give away to everyone and the reciver could use that Breath to awaken. As I said before the Breath keeps in itself all the needed part to Awaken, Hoid is not special in this....Everyone could awaken if you gave him breath

As I said the most Spren would be disgusted by it, but this is not an hard limit. A willing Spren could still make a Nahel Bond with you...It's just really really unlikely. IF Nicrosil could store Stormlight and IF Stormlight stored with Feruchemy loses its leakly nature. It's possible to stock a decent amount of Stormlight into a Nicrosilmind, of course the amount will be limited by the metal's amount...So you will not have an unlimited Stormlight storage. Notice that as we don't know how much Investiture-worth the Stormlight is..It's possible the Nicrosil would be filled up with a relative little amount of Stormlight...as we didn't ever see Kinetic Investiture stored with Feruchemy, everything is possible

I think this is the exact "perception issue". The Royals not in the right lineage believe they can't have the Locks and this stop them for having the Royal locks

Perception is a great deal here, in theory they will be unable to do unless someone convinces them they could do it

I don't believe the Last Legion's flee was part of an Odium's Plan. They Simply took an opportunity. Odium at that time probably doesn't care of losing some minion, in the great scheme loses some Listeners was not a great deal. About the healed-parshmen, the so called "Voidbringers"..I believe they are stable as they are. Honestly I can't know if their status is the result of an bad made bond or if simply the Everstorm is unable to heal them and Bond them properly with a Voidspren at the same time. The second Everstorm's passate will be really relevant. Butfrom the reports we had, some Listeners turned into Forms of Power. So also if not automatic, some Parshmen turned into proper "Voidbringers" (unless those were DullForm Parshendi Hidden amoung the Parshmen). For now, I believe a Little fraction of the Parshmen were in the right conditions to successfully change Form, the rest becomed some Void-Dull Form (without a Better term)...they messed with the Form's change and this is the result.

You will simply store (if it is possible at all) Stormlight not Breath, by the way...We don't even know if you could store Kinetic Investiture into Nicrosil so It's possible you can't store Stormlight either. As long as the Spike remains I think you will be unable to heal the crack and the Spike would repel/disgust most of Spren. I am not sure about what kind of healing are you refering to, The Spren fill the crack with himself, but the Crack in the Soul are still there

Like weltall said Vasher could not stock Stormlight ad he does with Breath. They have simply a different amount of stickyness. Vasher doesn't neither Need an huge amount of Breath to survive on Roshar. 1-2 Breath for years (and Just when the calendar is aganist himself) is enough for him to survive. For the rest the Stormlight is so freely avaliable to not worry. Vasher is also suppressing his Divine Breath in Roshar and He probably carry in himself not too much Breath or He becomed good to Mask them. We already saw someone capable of goiing around with 100-200 Breath in Roshar wihtout expose himself...so no really hard to believe. On a last note, people on Roshar has no experience with Biochroma and they have not Breath to start... for them is really harder to notice someone else Biochroma compared to a Nalthis guy.