Your DM casts "Are you sure about that?"
I vaguely remember a perk in some expansion book of some Shadowrun edition that was basically "common sense" and ruleswise it meant that once per game session the GM should ask you "are you sure about that" when you're about to do something stupid. That's it. If you go ahead, you go ahead. If you don't realize that they are triggering the perk, you go ahead. If you never do anything stupid (yeah, right), they will never ask.
I tend to give that to my players "for free", but I still love that it's been encoded as a perk that's worth some points at character generation.
That's also a core rulebook perk for Vampires: the Masquerade
It does make sense. Players aren't their PCs, they don't see the world as their PC does, so things that would be obvious from their PC's perspective aren't necessarily from the player's. That disconnect means there are bound to be times when players do stupid stuff their PC wouldn't actually do, so a nudge from the GM can set them straight
It also exists in GURPS:
Common Sense
Cost: 10 points
Common Sense is a mental, mundane advantage that results in the GM making a Will roll when you have your character start to do something the GM feels is stupid. On a success the GM can warn the player ala “Hadn’t you better think about that?” (Basic Set 43)
The Wizard says, "Yes, I'm an Evocation Wizard so I use Sculpt Spells to choose all my party members. They automatically make the save and take no damage."
That's a nice way to replace a boring, old tomb with an exciting, cool mushroom cloud.
So Fireball makes a 20ft radius sphere. That’s a sphere with a volume of 33,510.322 ft^3 A sphere 100 times bigger would be 3,351,032.2 ft^3 Such a sphere would have a radius of 92.832ft The range of fireball is 150ft, so you could safely cast it’s 100x magnitude counterpart. Of course this is a very simplified idea of what 100x magnitude fireball could do. For instance, does it do 100x the fire damage? ~2,800? That’s over 50.9x more than lava (which is ~55). Does that mean it’s 50.9x hotter than lava? Making it 35,630-61,080 C, 6-11x hotter than the surface of the sun? These calculations are all fast and loose as actual explosion calculations are too complicated for my little brain.
When the DM starts rolling 800d6, you need to cast jump and jump 3000ft away.
If a massive fireball hits you, just shout “I do not consent!” If someone who will survive the blast hears you, they are required to spread the story at every tavern they go to.
The slight DM pedant in me is torn about how you chose to interpret the size of the sphere.
There is absolutely no reason to not use volume as the thing being modified by the item EXCEPT as far as I am aware the RAW is that the fireball is measured by its radius.
By that reasoning the new fireball should have a radius of 200 ft. Which is obscenely large and also puts the caster within the blast radius.
If I remember correctly in older editions the fireball would also fill up rooms until it's full VOLUME was achieved not necessarily just it's radius.
Meaning a 20ft radius fireball would fill a 5ft x 5ft hallway/tunnel (weird size I know... easy math) for 1,340ft and the new 200ft radius (33,510,300 ft^3) fireball would fill the same hallway for... 1,340,412 FEET OR JUST SHORT OF 254 MILES OF TUNNEL!
If my players were stupid enough cat fireball on a magic enhancing object, personally, I'm using the later object and also multiplying the damage by 100.
Their new party can start by investigating the massive village size crater recently discovered by the locals.
Sounds a lot like https://en.wikipedia.org/wiki/Centralia_mine_fire
Ok, now I want a XKCD style "What If" comic about this...
Let's just say it does 800 d6 damage and call it a day.
Such a sphere would have a radius of 92.832ft The range of fireball is 150ft, so you could safely cast it’s 100x magnitude counterpart.
Maybe I'm stupid but I don't see how you could safely cast it. Even if you cast it all the way back at the edge of the range you still would be inside the radius.
You target something 150 ft away, and it reaches 93 ft towards you before dying out
The radius is the size of the sphere as measured from the center of the explosion.
Maybe this analogy helps.
You throw a ball at a wall and it bounces back towards you. If the ball reaches you or passes you then you die.
You can throw a ball (the fireball) 150ft. At the end of your throw it hits a wall (center of explosion). The ball bounces back towards you 92.832ft (explosion radius/edge of explosion). The ball is now 57.168 ft away from you. Ball did not reach you therefore you live.
An evocation wizard could safely cast it.
How much thermal radiation does the fireball hit you with at that distance?
A very similar situation happened in an old campaign of mine where the player had some fair warning about consequences but went and did a thing that blew up a fucking moon of the setting.
The environmental consequences alone defined the next few generations of the setting. I just rolled with it and after a while I went from
to 
Soooo they blow themselves up, because it amplifies their magic a hundredfold? :D
From my experience Fireball times 100 is leveling a nice city block.
Bro is leveling the entire city and surrounding countryside
they cast "the unmatched power of the sun"
Wizard: “I say we nuke the whole site from doorway. …it’s the only way to be sure.”
Somewhere there exists a list of all TTRPG war crimes ever committed. Honestly, depending on location, this one could be anywhere pretty high on that list, but probably not in the top 100.
you can't just introduce a gun in the first act and not expect the players to shoot it in random directions
B-but I didn't conjure anything! It was an evocation...
Okay but a Sorcerer with Careful Spell could make it work
Or an evocation wizard
Careful spell doesn't prevent damage, just ensures you take half: 800d6 / 2 in this case. You're thinking of the sculpt spells feature from the evocation wizard school.
Would a careful spell also be affected by the finger? And if so would 100x half be 800d6/50 or 800d6/(1.26 E30)?
What it do
800 d6 damage.
Complete answer: https://lemmy.world/comment/3129632
Vas Corp Bet Mani
Tbh is the dm that had the dumb idea of putting that object there... What good would it do storywise?
It's a powerful weapon to use in a safe situation, but you also must keep it safe until that moment. Adds difficulty temporarily and then it's an absolutely astonishing grenade. Throw it at a dragon with magic and watch it burn itself to death. Or be careful to not use any small magic (tough for puzzles and stuff) in order to have a super dangerous weapon.
Also you can just make up something that nullifies it that some enemy brings and it never works again after that, like the main enemy of the dungeon it was found in or so who had hoped to act as a trap to kill you with it (just like these characters probably did)
