Are you a magic user? If so, you have the Mother of all Magic to thank: Mystra. Her story is bonkers.  She is the second incarnation of the Goddess of magic after number one, Mystryl, sacrificed herself to stop Karsus, a temporarily self-created God that absorbed the knowledge of the Universe and said “Fuck, I have regrets,” destroyed the weave temporarily ending all magic, then reincarnated as Mystra seconds later in order to recreate the weave in order to help save Karsus’s people from being destroyed. 

Later, she was murdered by the Guardian God Helm during the Time of Troubles.  This Age of Fearun history deserves its own  article which you can find here. To summarize, Ao the Gods of Gods, got pissed about the other Gods wanting power and being overall dicks to their own faithful. (Thanks Bane and Myrkul) So Ao forced all the Gods to walk with on the earth like mortals.  This caused divine magic to cease working, arcane magic became unpredictable to use (think Wild Magic) which was Mystras domain, and now all the Gods walking the earth became mortal.  Now what’s really cool about this is that they made this scenario into an actual adventure called Shadowdale, made by Ed Greenwood For TSR back in 1989.  I don’t want to ruin it for those who wish to play it one day, but

—————-SPOILERS—————-

Mystral was thrown down with the other gods and was immediately captured and tortured by Bane, The God of terror, hate and all that evil bullshit.  Wisely, she enchanted a large portion of her power into a pendant and gave it to the third reincarnation of Mystryl, Midnight. (this shit is confusing I know, just go with it) Midnight, who was just a favorite follower of Mystra at the time, kept it safe for her, and accompanied a band of heroes to free Mystra from Bane.  Midnight gave Mystra the pendant, Mystra became powerful again, opened up a gate to the Celestial Stairway that linked the Realms with the planes, which was guarded by Helm.  Arguments were had, Mystra got pissed, and then…

“he attacked him with bolts and beams of energy, fire and ice, mystic blades and magical hammers, and dread creatures with fangs and claws, coils and maws, wings and tentacles. Helm held firm, absorbing or brushing off each of her assaults. Weeping blue-flame tears of anger and frustration, she grappled with Helm and fire leaped from her mouth. Helm held her off with one hand and raised his visor. As their gaze met, Mystra let out a terrible scream heard across the Realms as she saw her doom written in his face. Helm drew back and punched his gauntleted fist through her chest and Caitlan’s body exploded in a blindingly hot flash of devastating power.” – wiki link

Midnight found the pendant at her feet afterword, and then became the next incarnation of Mystra by Ao himself.  Later, in 1385 DR, Cyric, the god of lies and deception, murdered her which ultimately caused the weave to collapse which created the Spellplague, a giant fucking storm of blue flame, where magic ceased to function for a decade, made magic users go mad or die, laid waste to entire regions, civilizations, cities, destroyed the World Tree, destroyed most Outer Planes, and gave Asmodeus the power he needed to throw the FUCKING ABYSS into the Elemental Chaos in an attempt to end the Blood War.  Lots more happened that fucked with the world.

To end all this bullshit, in 1479 DR, a super old wizard dude named Elminster encountered the the last remaining presence of Mystra which possessed a bear that guarded a cache of items, and helped her with some quests that ultimately revived her and became a goddess again in 1487. 

So what can she actually do?

Technically, Mystra is the strongest God of all time but was neutered in order to not rule the universe or push her way around.  She can cast any spell at maximum level, shape change at will, grant other other creatures spell knowledge, and can basically access and control the weave.  She could do basically whatever she wanted with magic. 

So you wanna be a worshiper?

You like magic? Like, A LOT? Sweet, then do we have a Goddess for you! The Church of Mystra preserves magical lore like some kind of Harry Potter Library just in case some bullshit happens.  Members like to recruit those with potential of highly skilled in magic.  We like to experiment with magical theory, create new spells, enchant magical items, and protect anything that has to do with magic. Magic Magic Magic.

Wanna use Mystra in a campaign? I gotchu

1. It was widely believed that the newly reincarnated goddess, Mystra, sent the notes on Karsus’s Ultimate Spell flying off into the multiverse, never to be found again.  Until now.  Stop the Cult of Evil Magical Bullshit from finding these notes on the Ultimate Spell and save the Multiverse once more.  Maybe even with some Mystical help from Mystra herself?
2. Rather than Elminster encountering the weak decrepit form of Mystra after the near century of her death.  She pleads with the group to help her become a goddess once more and restore the weave back to its original form from before her death and the Spellplague.  The side quests can be up to you or go by the book series by Ed Greenwood, Sage of Shadowdale.
3.  Legit just play the Shadowdale adventure made for second edition dnd.  Of course it may need some heavy revising by the plot and setting are still there to use!