D&D 5E Quasi Magical Nukes?

[SkidAce]

Don't forget structural damage.

I would use high level spell analogues;

Instantaneous Sphere of Annihilation at ground zero (thousands of feet)
Radiant damage (sunburst?) 1st mile out
Firestorm next mile radius
...with lingering necrotic from ground zero to full radius...

There is plenty of info on the affects of such weapons, to give you an idea of the size.

However, in game terms [MENTION=19675]Dannyalcatraz[/MENTION] is correct, you can story/rp/handwave most of it.

Perhaps give some lingering necrotic that can't be cured and uses a disease track with a high DC to survive the stages and get better, if you want survivors to deal with the after affects.

 

[MechaPilot]

I generally agree that it's not needed to come up with the mechanics for the actual nuclear explosion itself. That's all pretty easy: fire for the heat, bludgeoning or thunder for the shockwave, and poison and/or necrotic for the radiation. Plus, it should probably just flat out kill anything and everything within a certain radius of the blast.

The only part I'd think would need any kind of mechanic would be the after-effects, for example, the effects of spending time in the irradiated area.

 

[Dannyalcatraz]

Good point.

 

[Ancalagon]

The book "the gnole" (which is an interesting and tripy read by the way) had an interesting scene that was the magical equivalent of a nuke - summoning the salamander, a powerful fire spirit/god that just burned everything in the vicinty . The main character, a shaman/sorcerer type, prepared the summoning as a sort of "if things goes wrong, destroy everything so it doesn't fall in the wrong hands" plan B.

Anyway, I think what's important is not so much the mechanistic details (it does 50d20 damage! no 100d6!) but rather the impact on the game world if it goes off and how this magical nuke works. This matters far more than the amount of damage because it directly impacts how it may be countered - stopping a portal to the positive energy plane is not the same as stopping the summoning of a fire god, for example. Knowing what the impact is also matters because it gives you more maneuvering room as the GM, because the heroes don't *have* to win. Will it destroy the world, or merely a kingdom, or a city? Even if it's "just" a city, it's a big deal (see Hiroshima). Will there be lingering effect? Will the destruction spread?

 

[SkidAce]

That's a great idea to differentiate between real nukes and these magical ones.

It keeps spreading slowly. Can only be stopped at the source (ground zero) where its all icky and magical radiation and devastation.

Grows slowly, like years for feet? Or grows fast, like hours for feet.

Interesting story potential here.

 

[Ancalagon]

Oh! There was an episode in Invader Zim where there was this enormous, city destroy explosion... except it spread very slowly. Like you could casually walk away from the blast wave, even pause to tie your shoes. I believed it was called "Walk for your lives"

I really do like the idea of having to walk inside the disaster to fix it.

There is also this notion - I've seen in in movies and also in the Dark Matter setting - that a nuclear explosion is actually a brief portal opened to hell. This could be what is inside the slow expanding "explosion"

 

[Mad_Jack]

I'm thinking, since you're planning to use crystals (and the Spelljammer thing), that once they're triggered, they glow with a bright light and a crystaline chiming sound and slowly start turning everything around them into crystal as well, in a radius that increases by X miles per day up to X radius...
Every living creature within the initial "blast" radius is instantly crystallized. Things outside the initial radius but within the expanding radius have X amount of time to either run like hell to get out before they begin crystallizing, or to destroy the crystal and thus stop the process. Everything turned to crystal remains so for at least a thousand years.
They're magically made from the same crystal as the crystal spheres themselves (originally designed to create new crystal spheres as a means of terraforming, never meant to be set off inside an already-existing sphere), and if you have enough of them or a big enough one, you can turn an entire crystal sphere into a solid glass marble floating in the phlogiston.
Ancient half-accurate whispers of the use of smaller-scale versions have given rise to the legends of fantastical crystalline cities and such. The migrations of ancient peoples may have been them fleeing the effects of such a device.

Depending on how you want to play it, perhaps the devices the bad guys have/are after are smaller versions of the ones that destroyed the entire world in a single night. Prototypes, or "backpack" nukes or something. Just big enough for them to lay waste to a hundred miles each.

 

[Quartz]

There's a Dragonlance short story about a nuke. It involved a gnome and a substance called Plus-gnomium, I think. Ironically, it's the forces of Evil who decide to not only not use it but deliberately lose it.

 

[Tinker-TDC]

For a nuke that heroes could conceivably interact with:

DC30 CON saving throw within x radius. (high save, but theoretically survivable)
On a failed save the target is disintegrated. (shadow on the wall)
On a successful save the target takes 10d10 radiant damage, 10d10 thunder damage, and 10d10 fire damage. (the light, the shockwave, the explosion)

If the target has full cover the blast is different:
On a failed save the target takes 5d10 radiant damage, 10d10 thunder damage, 10d10 fire damage, and 10d10 bludgeoning damage. (the light, the shockwave, the explosion, the debris)
On a successful save the target takes half damage.

That's for a narrative usable bomb, though. The big thing is radiation, though. Basically, I'd put it up as different overlapping layers centered on the explosion stretched for wind and the rotation of the planet. Each layer is (let's say) about 100ft bigger than the largest layer it engulfs and is dc11 CON save every minute or take 1d8 necrotic damage and 1 level of radiation poisoning (on a successful save take half damage and no radiation poisoning). For every layer increase the DC by 1 and add an additional d8 necrotic damage.

Example:
1,000 feet from the blast (I know fallout would be more than a thousand feet, but this is for the concept, not the direct 1 to 1 comparison) it is CON11 or d8 damage.
900 feet from the blast it is CON12 or 2d8.
800 feet is CON13 or 3d8.
500 is CON16 or 6d8.
the center would be CON21 or 11d8.

Radiation poisoning is just a level of exhaustion (that is, it stacks with exhaustion) that can only be removed with Greater Restoration or some equivalent.

An alternate radiation poisoning is just having the necrotic damage reduce the target's HP maximum by that amount.


For every month that goes by add a minute to the time between radiation saves (ie. a year after the blast you save vs. radiation every 12 minutes rather than every minute. After 5 years you save once per hour, etc.)

 

[transtemporal]

It kinda depends on what you what the nuke to do. Is it a wooden building destroyer? 20d10 damage, no save. Is it a city destroyer? 200d10. Is it a nation/continent/planet destroyer? 2000d10+ baby! I don't think its necessary to model it further than that. Everything else is just special effects.