Chapter 1: Explanation
This idea came to me when I answered a question on Overlord subreddit.
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Question
You're transported to the New World but aren't allowed to appear in Nazarick (you appear the same time as Nazarick does). You have all the knowledge of the series that we know so far and are allowed to bring 3 items you own. Where would you appear and what will you do with your knowledge to survive?
My answer
To begin I assume that the three items are World Class Items.
To begin are you a player and what's (or what would be if you were a player) your level?
Anyways it doesn't matter for my plan.
I would choose 3 WCIs: Seed of World Tree if I'm not a player (if I'm a player I would already be from an heteromorphic race) otherwise World Saviour (as with time it grants absolute power), Downfall of Castle and Country and the WCI that could negate its effects according to Ainz. Seed of World Tree to change my race into an heteromorphic one (True Vampire Lord or something as long as I stay humanoid and become immortal).
As an immortal myself, Nazarick would always be a thorn in my side (thanks Albedo, Demiurge,...) since they would conquer the whole world (I could not change this decision as I couldn't prevent Ainz from spewing bullshit in front of Demiurge) and I don't want to be an eternal vassal. I would firstly appear in the Empire and take control of Jircniv and Fluder (easy peasy with Downfall of Castle and Country). I would use the Empire to send a letter containing the location of Nazarick and a description of its inhabitants strength and alignment (just lies to make them a general and big enough threat but one that could be overcame if they give their all together) to Slane Theocratie, the Kingdom, the Council State and everyone reachable. I would even encourage them to ally with the demi-humans for this cause (with copious amount of mind control obviously). I would tell them to be overly cautious as there could be doppelganger spies anywhere. PDL in face of this great threat would use the Eight Greed King treasury to arm this croisade. Ow, I would have also either enslaved or killed Renner (I don't want any threat beside me and she's too smart to be let at her own devices). Now Nazarick doesn't know that there's a croisade coming their way. Ainz would continue being Momon the adventurer. I would send a squad to where Brain and his bandits were hiding. They would mind control Shaltear with many death on their side (I wouldn't go myself as for my plan to work I should never be seen). I would perfect this control once she's already in her semi controlled state obviously. I presume that she would still appear as red in the guild members list. This is where the game begins. Shaltear and some DLs would be sent to confront Sebas and Solution. Sebas would be enslaved and Solution imprisoned (if she was also enslaved it won't work for the rest of my plan).
When Ainz would confront Shaltear and Sebas they would say that Touch Me and Peronroncino programmed them to destroy Nazarick if the guild either wanted to conquer the world. It's in line with Touch Me behavior and Peronroncino could have been dragged along (for shit and giggles). Albedo won't accept this (as she is crazy). The rest of Nazarick won't know what to do as they couldn't go against either of the Supreme Beings. This would be even more pronounced as Ainz will decide to let them live and to stop all they were doing for their conquest (he always put his friends over all). He would question his way (he didn't even know that they were conquering the world) and would put Nazarick in a passive state. Albedo could always go crazy and try something but alone it won't work (she doesn't have her squad yet).
This time lapse would allow me to finish the preparation for the croisade. Each soldier would be ingrained with this sense of duty same as Paladins and won't hesitate to give their live for this war.
In the meantime I would accumulate knowledge from all over the world on magic, martial arts,... and get stronger if I can (I would try killing for exp and if it doesn't work I would try training).
Then a general attack would launched with at its head Shaltear, Sebas, the Black Scripture, the different DLs. They would know the layout of the tomb thanks to me, Shaltear and Sebas. Even though it would be changed after their defection, major change cannot be done. Just before the attack I would kill Solution to tie any loose end. It could also cause a distraction in Nazarick.
With this it would be an epic battle with four possible outcomes:
1- The best option for me: Mutual destruction. I then come and enslave the survivors and then I became the eternal ruler of the world. The world would be heavily affected and could even go backwards technologically and magically. This is why I acquired all this knowledge beforehand. Anyway I am immortal (even if weak).
2- Second Best Option: Nazarick wins and I could take on the survivors myself. It would then go back to the first option.
3- Third best option: Nazarick wins, they are still too strong for me and Ainz is still alive (or is resurrected). He would see all this destruction as his fault and won't ever accept to conquer the world again. I then go in seclusion and prepare the next croisade otherwise it would be boring.
4- Worst option: Nazarick wins, they are still too strong for me and Ainz is dead and could not be resurrected. I hide for some centuries and then go out to look at the destruction the NPCs brought upon the world. I suppose there won't be any big settlement standing anymore. The NPCs who are not Heteromorphs would be dead from old age. If the living NPCs went back in seclusion after this onslaught of destruction, I would start preparing the next croisade. If they are still dictating their laws and I couldn't take them on one on one, I would live as I could creating rebellion here and there for some millennias. It would either wear them down or bore me. Anyway it would be interesting.
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When I imagined this development, I thought that it would do an interesting story if well-written. But, I hate writing. When I start a story I imagine a plotline from start to end and then became bored of it. I have this problem for many years now. As I could not write the thousands of stories I imagine this book will contain my ideas for fanfictions. If any of you ever come to be inspired by one of my ideas and write a book, please inform me.
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Most of my ideas would depict a person neither good nor bad, really selfish with loose morality. So no wannabe hero or edge lord.
CREATORS' THOUGHTS 
Evil_For_the_WIN
Evil_For_the_WIN Hello. This is it. If you have any scenario you want me to develop, please share it in the commments. I hope someone would one day make a story from my ideas.
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