D&D General Help making my big bad villain who wants to rid my D&D world of all magic

[Criles]

So, who I plan on making the big bad of my current campaign (a powerful wizard who tapped into the magic of the void and is almost invincible [ofc not really cause they need to be beatable] when it comes to magic), I want to give them the goal of trying to absorb and basically 'delete' all magic in the universe other than theirs and themselves, making them the sole magic user and holder. But, this is D&D and I want a huge epic final battle and it will be hard with no magic! Basically, what this villain is doing is going under the disguise of this omniscient being that stops really powerful magic disasters, users, or monsters (that they create and put into play) so that they can convince everyone to reject magic (all magics arcane and divine). But I just don't know what to do to keep this idea going, I would really appreciate some help!
For more context, this villain is from a different dimension (which has been a big part of this campaign's story and theme thus far), and basically somewhere along the line they got a bunch of the higher beings from their universe together in one place which caused a rip in space and time, causing a tunnel that transported them all to the setting's universe, however when the tunnel closed back up, the villain got stuck in the dimension tunnel and went mad from being stuck in their for six years, which probably felt like an eternity to them. They got so powerful off of the tunnel's energy that they are an expert with basically all magic. The party, convinced by some of the devils and fiends from the other dimension, reopened the tunnel, letting a being of pure white light (the villain's form due to the exposure of the tunnel) be released who absorbed (or more like drained) the higher beings and their magic as soon as exiting the tunnel. But now, the villain is taking back their original form and is hiding right under the party's noses.
Anyways, that's definitely a lot, but I just really love the idea and have a plan to have the party go up against these great magical threats (which are being orchestrate by the villain) until eventually they discover who the villain is and have to face them, but I'm not sure what to do for a big bad fight if this being with their magical powers is stronger than a god or even a great old one.

Thanks!

 

[Leatherhead]

In which edition?

 

[Coroc]

Maybe use beholder anti magic eyes somehow?

Combined with an artifact that absorbs spells?

Insert some no magic zones also, and eventually wild magic zones, where all the magic is "stored"

 

[Aelryinth]

You are probably going about it backwards.
What I would do is keep the big bad exactly the same, but change the players to people who don't use magic, i.e. fighters, thieves... and people who use technology and/or psionics. They go out adventuring to rid the world of all these magical threats with a mysterious patron, for 'all the common people'... but as they get more powerful, their patron realizes they are really too good at the job, and starts trying to get them killed as they fight the ongoing catastrophes, realizing they post an 'anti-magic' threat to his hegemony.
In the end, his scheme WORKS, and he's the only one who can use magic... and the party, who doesn't use magic, is the only one who can bring him down.
The campaign would wrap up on the party deciding to let magic and all its good and evil back into the world, or change things so that people have to follow the roads they laid out.
The key theme to the PC's is that they use powers that 'anyone' can use, so no exclusivity, no gifts, no bloodlines, no divine patronage.
If you do it this way, the campaign should almost write itself. You don't have to worry about the anti-magic, it's built right into the non-magical PC's. Just tell them straight up at the beginning of the campaign they have no ability to use magic, so any magical abilities they might get from leveling, they simply can't use. Then tell them what is not magic, and go from there.
=== Aelryinth

 

[OB1]

@Criles As it get's closer to the time to confront the big bad, the PCs magic begins to falter. They learn of 7 powerful magical artifacts that can counteract this, and go on a quest throughout the multiverse to acquire them, giving them the power to confront to BBEG.

However, it was all part of BBEG's plan. She needed the items found and brought to her (as gods prevent her from entering the planes where the items exist) to complete the plan to gain control of all magic. When the PCs arrive at the tower, the BBEG's minions attack with the sole goal of taking these items from the PCs.

If the minions succeed, PCs no longer have access to magic in the end fight, but have ways to regain control of the objects and thus their own magic before the items are destroyed. If the PCs succeed at keeping the objects, BBEG flees to another location (without the power of the lair actions in location 1), but PCs face a few more fights from minions along the way, all trying to take the items, and if successful, BBEG immediately attacks the PCs.

Give the PCs ways to discover this plan ahead of time. Perhaps they think of a way to deceive BBEG and spring a trap on her, perhaps they think it's the only way and go in willing to sacrifice everything in the hopes of saving the multiverse.