…as for what you mean, without the E lement s , there was no other way to bring Luna back.  So in the timeline where Discord is brought back and uses Celestia and Luna for amusement, maybe the price to bring her back was the E lements …

…[Luna] could have been reformed somehow, perhaps at great cost to Celestia, maybe the Elements themselves.  If Discord of all beings can be stopped in the other timelines, why can't the same hold for Nightmare Moon? 

…even if the somehow could separate and give body to her without messing with Luna or Rarity (her two possession victims so far) she would still be evil…

Note that in my original piece, I said "could havereformed" and not "couldreformed".  I wasn't trying to imply that Nightmare Moon would have been reformed like Discord, Sunset, or Starlight was, but apparently, I didn't get the message across. I suggested that.  Actually, I said it in a previous comment:I don't adhere to that headcanon about Nightmare Moon coming from an external source (I know it's what the comics say, but I personally don't treat the comics as officially canon, even the good stuff), but I see what you're saying.  However, that does bring up a discrepancy.  I've always held that Nightmare Moon and Luna were one and the same, just being different facets of the same character, but I can see you don't follow that notion. To put it in the terms of the "Nightmare Moon as external force" headcanon, in these timelines where Nightmare Moon doesn't show up, Celestia could have used the Elements herself to rid Luna of the Nightmare Forces (or whatever you want to call it), perhaps at great cost, maybe even the Elements themselves. Though, a good point was brought up that perhaps Celestia had toLuna in order to get rid of Nightmare Moon, possibly leaving her jaded after the fact.  That may be why she took a more proactive approach against Sombra (I understand war is war, but it's a bit strange Celestia would resort to total war to fight Sombra's forces) and why the Changelings were ultimately successful in the end.  Maybe having to kill her own sister for the good of Equestria emotionally burdened her to the point where if another threat were to come her way, she would either be emotionally unprepared (a la the Changeling Resistance timeline) or hellbent on making sure her country was safe (a la the Crystal War timeline).Heck, it even works in the Flim Flam Industry timeline.  After her encounter with Nightmare Moon, she probably didn't have as much in her to rule, and she kept making poor decisions while resulted in an economic collapse.  All of this is wild speculation, however, and it's entirely possible that Celestia found a way to bring Luna back, though through compromising something in the process.