The closest would be: The Infinity Gauntlet

Its your world - if you need an Infinity Gauntlet, make an Infinity Gauntlet. Obviously, you can rip-off Marvel as much or as little as you want (providing you don’t infringe their IP, which you won’t do unless you publish it). Infinity codpiece, anyone?

It would clearly be an artifact so you can look to existing artifacts for inspiration starting on p.219 of the DMG but you can give an artifact whatever powers you want:

An artifact is a unique magic item of tremendous power,
with its own origin and history. An artifact might have
been created by gods or mortals of awesome power.
It could have been created in the midst of a crisis that
threatened a kingdom, a world, or the entire multiverse,
and carry the weight of that pivotal moment in hi story.

Some artifacts appear when they are needed most.
For others, the reverse is true; when discovered, the
world trembles at the ramifications of the find .

The closest thing I can think of is the Maze Engine

In the dnd5e module Out of the Abyss it says the Maze Engine is...

a mechanical, magically powered device capable of altering reality. Modrons refer to the device as an Orderer because it was designed is to bring order to chaos.

In the campaign itself the Engine is

damaged, irreparable, and precariously balanced above a river of lava, severely limiting its usefulness,

but it could work as a plot element.

Some of the listed effects are

• The engine emits a flash of golden light. All magic items within 300 feet of the engine are destroyed, except for artifacts, which are cast into the Astral Plane.
  


• The engine emits a bright flash of white light. All player characters are transported back in time, as they are now, to the moment when the adventure began.
  


• The hollow interior of the engine flickers with crimson light until the end of its turn, whereupon one dead character or NPC of the DM's choice is restored to life, as though subjected to a resurrection spell.
  


• The engine emits a flash of green light. Each creature in direct contact with the engine must succeed on a DC 18 Constitution saving throw or take 10d6+40 force damage. If this damage reduces the target to 0 hit points, it is disintegrated.

Given the nature of these effects, one could imagine (and a GM could decide) that a working Engine could accomplish what you want.

The closest thing I am aware of from anything even tangentially-related to D&D is from Rich Burlew’s vaguely-D&D-3.5e-inspired comic, Order of the Stick. In that,

Vaarsuvius agrees to an infernal deal in order to save their family from a black dragon whose child V had killed in an earlier arc. Hell’s side of the bargain is a “soul splice,” which isn’t actually a thing in D&D, giving V the power of three of the most powerful spellcasters whose soul found their way to Hell. They save V’s family by casting one of the soul’s signature spell, familicide, on the dragon, killing her and her entire bloodline, ancestors and descendants.

That spell also doesn’t exist in any D&D canon, but as an epic spell in a world loosely based on 3.5e, it would have used 3.5e’s “Epic Spellcasting” system, an open-ended system wherein custom spells of immense power could be built—making this a plausible spell in that system even if it was never actually printed in a book. Epic spells are more powerful than 9th-level spells, and so would supersede wish. However, since Epic Spellcasting is irretrievably broken, it is very unlikely that D&D 5e will ever implement it or anything like it.

So something as powerful as described would not be possible in D&D 5e outside of divine intervention or an extremely generous wish.

Great thing about DnD is that you, as the DM, can do whatever you want.

I'm assuming, of course, that you don't want to be cheesy and state "This BBEG Wishes for something terrible and is lucky enough for it to work".

But nothing stops you from creating a legendary magic device (let's say a gauntlet) that allows the user to cast a "Perfect Wish" free of the limitations the Wish spell usually has.

The scope is fine. The targeting is finicky.

In the lore? D&D has plenty of cataclysms, but they tend to be "catastrophic effects on an area" rather than "catastrophic effects on a race".

• Eberron, the Day of Mourning, turned the land of Cyre into a place where no living thing could grow, and killed off basically everyone who was there at the time.


• the Forgotten Realms has had a great many cataclysms over the years. Many of them have changed the way that magic works, changed the ways that gods worked, and/or had devastating environmental effects.


• Dark Sun had Athasian Dragons, and the ability to become dragons, and the horrible rituals that had to be gone through to do that, which mostly seemed to involve swallowing a bunch of obsidian and sucking the life out of an entire city over the course of a few hours.

So, magic of that scale does exist in D&D. It generally requires a lot of power - a ritual where many powerful mages sacrifice their lives to empower the spell, or a ritual put in place by a god over a number of years, or a large amount of expensive magical resources assembled by a very large number of middling mages (which then fails catastrophically) or... things like that. Generally speaking, single artifacts can't do it, but "needs this artifact" is often the sort of requirements that gets attached to rituals like that. Cataclysm-level effects are definitely in lore. The trick is the targeting. D&D does have race-targeting effects (Bane weapons, as an obvious example) but it doesn't generally have anything that would target a specific group over a wide area.

That's not to say that there's nothing out there. If the group already has some fundamental thing in common, they might be hit as a side effect. For example, the spellplague in Forgotten Realms did bad, bad things to people who tried to cast too many spells. A whole bunch of wizards died, but it wasn't because something was done specifically to attack wizards. Similarly, if you had a race that was especially vulnerable to the Far Realm, then bringing the Far Realm closer into conjunction might do terrible things to pretty much all of them.

More generally, though, these are all one-off things, that occurred at some specific point, in response to a specific extreme situation. The Spellplague was unprecedented... until it wasn't. If you're going to add a cataclysm at that level to your own campaign world (ritual-driven or otherwise), you should be customizing it.

There's nothing exactly like this in 5th edition

There's nothing in any D&D 5th edition product that will give a player character this sort of unlimited power in a reliable way. Wish can't do it, Divine Intervention can't do it, and even lesser deities like Tiamat don't canonically have any way to do it. That suggests you'd need at least a greater deity, but in 5e they don't interfere with the world.

• If someone in the world still has a D&D 3e era epic spell, that could do it. Rain of Fire, for example, will kill just about everybody within a 2 mile radius, and you could make a more powerful version with specific parameters. You normally need to be more skilled with magic than a human can normally get in 5th edition in order to cast one of these.


• Releasing a sealed elder evil or entity of primal destruction like Tharizdun is within the ability of a D&D character, and Tharizdun is canonically defined in D&D 5e, although his exact powers of destruction are perhaps less defined in 5e. The drawback is that Tharizdun is likely to destroy everything. Kyuss, the Worm that Walks, will kill all humanoid life but at least allow undead to survive.


• A disease or plague might wipe out all of a certain race or the people in a certain geographic area.


• I think this answer is the best. When you're the DM, you aren't limited to what's in the sourcebooks like players are.