Given glyph of warding, a book, unlimited funds, and enough time, I'd like to create a superbomb.
My goal here is to create a book where, only when I wanted it to, would detonate, dealing 100 fireballs worth of damage to everyone near this extremely explosive book.
The original wording for the trigger I was going to go with would have been a glyph on the cover with the trigger "when this touches the ground" and glyphs on each page with "when this takes fire damage", and then throw it on the ground far away from me.
This doesn't work because the spell targets the creature that triggered the glyph (me in this instance).
If I reword the cover to "when a creature other than [my name] touches the book" and keep the pages at "when this takes fire damage", does this solve the problem? Will the book then target that creature with all 100 fireballs? If not, what have I missed?
Best Answer
Yes, this would work
The way you have the trigger worded is perfectly valid and will result in the creature getting hit with all 100 fireball spells in/on the book.
I would tweak the pages' trigger to say "when a creature causes these pages to take fire damage" just to be extra clear that the creature that triggers the cover also triggers the pages.
However...you can't move the book more than 10 feet
Glyph of Warding says:
So, with this trick, not only will you have to spend 100 hours and 20,000 gp on the spells needed, you will also not be able to move more than 10 feet the entire time. And then you have to hope that your enemy comes to you.
Certainly with enough planning, preparation, and a lot of luck this could be a strategic play. However, there is almost no chance that this strategy will work for the average adventurer.
Will using a portable hole help avoid this? Up to the DM.
Object/surface in a portable hole (or other extradimensional space)
It has been proposed that you might be able to get around this by using a portable hole or some other extraplanar storage see (this Q&A). This might work, except a portable hole is 10 feet deep so removing an item from it would still trigger it.
Also, a DM could argue that the extradimensional space of the hole is an infinite distance away from the current plane. Thus, taking it out or putting it in the hole would break the glyph regardless. So this comes down to a DM decision to make that call.
Triggering object/surface while still in a portable hole (or other extradimensional space)
Another way would be to mount it on a surface inside a portable hole. It is very open-ended what is considered a surface for this spell (see this Q&A) but mounting it to the side of the extradimensional space is probably perfectly acceptable. Of course, since you can't move the surface/object out of the space (see previous section) you are not limited to triggering while still inside the hole.
And this should work as expected (assuming you set an appropriate trigger), doing damage so everyone and everything in the blast radius of the fireballs.
However, I would be very cautious since the portable hole is an object made out of cloth per the description:
Thus, it would potentially not be terribly hard to destroy with 100 fireballs worth of damage being triggered inside of/around it (since fireball's radius well exceeds the portable hole's dimensions).
Bottom line: it will be up to the DM if and how well any workarounds work
There are probably other ways around it, but you'll need a DM to likely agree to whatever workaround you come up with. And if they do watch out because...
Sounds like a great tactic for a villain!1
While this strategy is likely never to work for an adventurer, it is perfect for a villain setting a trap. If a DM is happy to let this work for you as a PC, they may be even happier to allow it to work for the evil NPCs as well.
1 - Thanks @Erik