So in Same Old World Lapis explains via flashback that she was trapped in the middle of the Gem War and mistaken for an enemy of Homeworld, leading to her getting poofed and sealed in the mirror that would be her prison for the next several thousand years. 

At the end of the flashback, however there is an odd little something that could be one of many things: the flash of light as the Homeworld Gems leave. 

I read a theory that suggested that this was a sort of “Gem Bomb” designed by Homeworld to kill off any gems exposed to it’s effects.  This may very well be true.  Context clues are very important here for discerning the nature of this flash.  Take Lapis’ quote:

“It soon became clear that there was no hope in stopping the rebellion.  All of the Homeworld Gems fled … in all the panic ofescaping earth, I was left behind.” 

Lapis describes the “fleeing” of the planet as a “panic”, suggesting that everyone was getting off-world as quickly as possible to avoid something, possibly the Gem Bomb that Yellow Diamond had decreed be unleashed on the earth. Flash forward several thousand years, and there are only a handful of non-corrupted gems on earth, Garnet, Pearl, Amethyst, Lapis, and Steven.  Now take Greg’s quote in The Return when he describes the Gem War’s conclusion:

“In the end, your mother could only save a handful of her closest friends.  If it weren’t for her shield, man, I don’t know.” 

The Gem Bomb, probably meant to completely kill gems, had an unforeseen alternate effect; Gem Corruption.  The bomb released an epic shockwave that traveled across the planet, ripping through every gem it touched, corrupting them to their very core.  The only gems that were exempt from the effects were those closest to Rose Quartz, both socially and physically. 

Rose’s shield blocked a concentrated blast from the Hand Ship in The Return, meaning it could probably protect those behind it from a planet-wide blast that would be much less concentrated.  The shield protected Garnet, Pearl, and Rose herself, while every other gem on the planet, save for Amethyst and Lapis, succumbed to the bomb.  The remaining Crystal Gems began to sweep the planet, poofing and bubbling their friends, storing them in the temple until they could find a cure for the bomb’s effects. 

Then, on a visit to the Kindergarten, a wild Amethyst appears!  Having stayed underground too long, she didn’t emerge until the Gem Bomb’s effects had dissipated.  The Crystal Gems then take her in, as surely there can’t be any other non-corrupted gems on earth. Lapis was exempt from the blast too.  Why though? 

Her mirror, designed to keep her imprisoned, acted as a shield of it’s own and protected Lapis from the bomb.  What she saw as a curse was actually the only reason she remained uncorrupted.  Which makes me wonder… is the Desert Glass from Steven’s Lion the same?  How many other gems were spared due to Homeworld imprisonment?  Only time will tell. 

I actually really like this theory - it's great!  Because it is evident that the explosion we saw is one we had heard of through Greg and these pieces of the theory fit very nicely together.  I would say the mirror saved Lapis, too.  It was an unfortunate imprisonment to be sure, but in the end, she may have existed otherwise.  So even though she hated it and hates it to this day, this could be a silver lining. 

If Lapis is a "reporter" gem like people are suggesting, she can definitely give us much clearer pictures (than Pearl) in what was going on during the war.  And images that may not be biased.  So thanks, mirror! 

Actually if I'm not mistaken it has 100% been confirmed that the Desert Glass' body is in fact the pillow.  A gem can take many different forms.  Corrupted gems just seem to not be sure of their holographic manifestation and some forms are just simply very abstract.  Similar to the Pyramid Temple, since that was its 'body' aswell. 

One quick theory though regarding Lapis' mirror. 

Lapis = Rose QuartzIn what way?Steven = Lapis' Mirror

It's very clear that when a gem is embedded into another object, it merges some of its digital information with whatever it can grasp. ( As to why Steven had those glowy veins and why he can fuse) Now, people are theorising that if Steven's gem is extracted, everything will be fine and dandy.  Wrong.  When a gem is extracted, the object takes sudden physical damage due to its data being separated from its source, deeming it useless. 

Actually if I'm not mistaken it has 100% been confirmed that the Desert Glass' body is in fact the pillow.  A gem can take many different forms.  Corrupted gems just seem to not be sure of their holographic manifestation and some forms are just simply very abstract.  Similar to the Pyramid Temple, since that was its 'body' aswell. 

One quick theory though regarding Lapis' mirror. 

Lapis = Rose QuartzIn what way?Steven = Lapis' Mirror

It's very clear that when a gem is embedded into another object, it merges some of its digital information with whatever it can grasp. ( As to why Steven had those glowy veins and why he can fuse) Now, people are theorising that if Steven's gem is extracted, everything will be fine and dandy.  Wrong.  When a gem is extracted, the object takes sudden physical damage due to its data being separated from its source, deeming it useless. 

Actually if I'm not mistaken it has 100% been confirmed that the Desert Glass' body is in fact the pillow.  A gem can take many different forms.  Corrupted gems just seem to not be sure of their holographic manifestation and some forms are just simply very abstract.  Similar to the Pyramid Temple, since that was its 'body' aswell. 

One quick theory though regarding Lapis' mirror. 

Lapis = Rose QuartzIn what way?Steven = Lapis' Mirror

It's very clear that when a gem is embedded into another object, it merges some of its digital information with whatever it can grasp. ( As to why Steven had those glowy veins and why he can fuse) Now, people are theorising that if Steven's gem is extracted, everything will be fine and dandy.  Wrong.  When a gem is extracted, the object takes sudden physical damage due to its data being separated from its source, deeming it useless.