Best reader, thanks for starting this post, but since it shall be long I will quickly summarise what will be discussed/questioned in this post. First of all this post is going to focus on Balin's unruining of Moria. This will be about which halls to unruin, the path of retreat from 2nd hall to 21st hall and they style of ruining to be done in the fixed areas and possible orc-dwarf battlefields. Secondly this post is going to focus on the style of ruining we currently have. This will be about how to create a nice ruining that makes sense and is easily reproducible. Thirdly this post is going to focus on the orcified areas. This will be about which areas/halls to have orc builds in, how to stylise the orc corrupted halls, how to stylise the orc creations (own made, so not natural or dwarven). Fourthly and lastly this post is going to focus on the balrog. This will be about what areas the balrog would have ruined and how that would have to be made, and posibble battlegrounds in moria against the balrog.

Now onto the first part Balin's unruining of Moria.
However before we can start this we need a few lore items, which I will list down under for all of you to read.
This raises the issue, which path was taken, thus which halls would be fixed on and around the path. Only things we know currently is that the first, second, third and twentyfirst hall should be partially unruined, however all other halls on the path are unknown. So for this I would like to ask you, esteemed reader, to help with planning a path through moria that the dwarves would take using the hall/cave list resource. (e.g. if you have your path contain the 2nd hall you add the number 4 to the list). This may include possible battlefields, such as the 2-3rd hall gate battle.

Now the second part, for the ruining, for this I think the best solution is to rebuild the halls almost completly then having small collapses and quite a bit of dusting for detail, this can best be seen in the 2nd hall. However, there are the issues of battlefields/orc overtaken areas, for the first I would propose to have it more heavily ruined and quite a lot of dwarven corpses, however for this we would need to create a concept first. The second one I will try to discuss in the orc section. If there are any idea's from people about how to do this, please comment below, as the more people that actively think about this, the better the result will be.

This is nice and dandy for the balin's path, however we also have a lot of other halls that we have to ruin, which require a different method. For this I would recommend first removing interior if it is food, partially removing/decaying if it is wood (aka full wood blocks get turned into slabs or 1/4th blocks) then start by having small collapsed areas in non essential parts, such as decorative ceilings/walls and separation walls. Thirdly I would say have small parts from pillars fallen off showing a stone layer underneath all the decorations and lastly dusting it like there is no tomorrow and spreading small piles of rubble all around.

Thirdly the orcified areas, this is something that is quite unknown, as in we only have orc cities and tunnels, but no indication on how to far to continue orc corruption into other areas, for this I think that the best solution is to look at it by a per case basis. However, the main rule should be that we should try to have spread out orcified areas as much as possible, as the orc population was immense during hay day, but have most abandonned now, as there was the battle of Nanduhirion/Azanulbizar. For style within halls I think that the 3rd hall is a good example, although minimal and for style within large caves there is a good example in the cave after /warp upper stairs. For the small orc caves there has to be more time spent into creating concepts, which again is something I ask of you best reader to help with.

Lastly there is the issue of the Balrog, where is he at this point, and which areas has he destroyed and how. For this there should also be a general path from the caves deep down to the 21st hall, which would be partially destroyed. The main area where the balrog would've destroyed halls are most probably the south east lower layers, and a few of the middle layers, with maybe one higher layer. However this also has to be planned beforehand, with caves/destroyed walls leading all the way down. This planning again requires some help as it is to much to do alone, so if you think you have a cool path to the 21st hall make a similar message as the Balin's path, but make sure that it is the balrog's path.

Now for style there is the gass explosion, this could be a possible style, however we can also go for a heavily ruined style. This is again something that has to be tested out, maybe in a possible themed build, or by people themselves (if you want a hall to see if you can balrogify on freebuild message me).

Lastly we have the battlegrounds of the Balrog, this is currently not something we can plan using the main map, as those will almost all be in the lower levels, however we can probably try to create a style already. This I would think would be heavy ruining and lots of corpses/defenses which are thrown about everywhere. Either way, discuss and try out if you want, any comment on this topic is appreciated!