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An exploit to circumvent the movement restrictions of glyph of warding is to cast the glyph on the walls of a demiplane or portable hole. As that space never moves, the glyphs can virtually be carried anywhere.

Assume that the DM rules that you can cast spells into or out of an open portable hole or demiplane, and that spell effects can target creatures or extend into or out of them. (And your DM does not allow the infinite simulacra loop.)

With a 15th level wizard and enough gold to pay for any required material components, what is the most damage against a single creature in a single round that you can set up per day of preparation (i.e. per long rest) by creating glyphs of warding?

Assume the creature has no resistances or immunities, and you have access to all published wizard spells.

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    \$\begingroup\$ We're also taking for granted that a creature can be effected by a glyph through a portal to another plain (eg the opening of a portable hole)? \$\endgroup\$
    – Michael
    Aug 12 at 6:18
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    \$\begingroup\$ @Michael Yes. I want to understand what the impact will be to assume that. I'll add it to make it crystal clear, this is what I meant by casting in or out. \$\endgroup\$ Aug 12 at 6:19
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    \$\begingroup\$ Related: Is there a minimum size for the Glyph of Warding spell? \$\endgroup\$
    – Michael
    Aug 12 at 6:28
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    \$\begingroup\$ Now this is the kind of D&D I came here to play. \$\endgroup\$
    – order
    Aug 12 at 12:34
  • \$\begingroup\$ I suspect Symbol and a stun or slowing effect might come into this equation... will try to figure it out. :) \$\endgroup\$
    – Senmurv
    Aug 12 at 16:44

2 Answers 2

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The maximum damage you can deliver is 732 per day of preparation

The Glyphs

As indicated in Matthieu's answer, we are better off using Explosive Runes rather than Spell Glyphs as Spell Glyphs expend an extra spell slot.

To get as many Explosive Runes as possible, we will follow a procedure that alternates between days:

Day One

  1. Cast simulacrum targeting ourself.
  2. Tell our simulacrum to cast glyph of warding with their 5th, 6th, and 8th level spell slots.
  3. Cast glyph of warding with our 5th, 6th, and 8th level spell slots.
  4. Take a long rest.

Day Two

  1. Tell our simulacrum to cast glyph of warding with their 3rd and 4th level spell slots.
  2. Cast glyph of warding with all of our spell slots.
  3. Take a short rest to use Arcane Recovery and restore two 4th level spell slots.
  4. Cast glyph of warding with the restored spell slots.
  5. Take a long rest.

Over the course of two days, we get the following Explosive Runes:

  • six 3rd level runes
  • eight 4th level runes
  • six 5th level runes
  • three 6th level runes
  • one 7th level runes
  • three 8th level runes

...totaling 183d8 for a maximum of 1464 damage over two days, yielding 732 per one day.

Note: If we have an odd number of days to prepare, we should just use all of our spell slots to cast Explosive Runes on the final day rather than casting simulacrum. This will give us more runes on that last day, since we won't have another day for where the simulacrum pays off.

Effective Damage

This initial damage calulcation assumes that the target fails their Dexterity saving throws, and that we roll the maximum damage for every d8. We can also calculate the effective damage based on the expected result of each d8 (4.5), and a couple of Dexterity saving throw benchmarks:

+0 Dex Save +5 Dex Save +10 Dex Save + 15 Dex Save
380.87 damage per day 329.40 damage per day 277.93 damage per day 226.46 damage per day

However, there are a few potential ways to improve this result with Spell Glyphs depending on the other ability scores of the target. I first tried other spells such as:

  • thunderwave and cone of cold to target low Constitution saves
  • chromatic orb to target low AC

...but it was almost never worth sacrificing the rune count unless there were absurdly high Dexterity saves, and absurdly low alternate stats.

The successful method, however involved debuffs. There are two main debuffs that can help us get more damage: bestow curse and slow (polymorph would lower Dexterity considerably, but unfortunately the spell ends once the new form takes any amount of damage, rendering it wasteful).

Bestow Curse

If our target has lower Wisdom saves than Dexterity saves, bestow curse may be able to give us more effective damage by causing disadvantage on the Dexterity saves. We would be sacrificing a 4th and 3rd level Explosive Rune for this Spell Glyph, but in some cases, that is worth it for the extra effective damage on the rest of our runes.

Here are the damage adjustments for a couple Dexterity and Wisdom save values:

+0 Dex Save +5 Dex Save +10 Dex Save + 15 Dex Save
+0 Wis Save -1.92 damage per day +19.67 damage per day +20.71 damage per day +1.19 damage per day
+5 Wis Save -8.09 damage per day +8.06 damage per day +9.71 damage per day -3.16 damage per day
+10 Wis Save -14.26 damage per day -3.55 damage per day -1.30 damage per day -7.52 damage per day
+15 Wis Save -20.43 damage per day -15.16 damage per day -12.30 damage per day -11.87 damage per day

In summary, bestow curse is worth putting in a Spell Glyph on the second day if the targets Wisdom save is particularly low (under 5), and the Dexterity save isn't particular high, nor particularly low (in the 5-10 range).

For all pairs of days following the first, the damage bonus doesn't come at the cost of those 2 runes, and we get the following damage adjustments:

+0 Dex Save +5 Dex Save +10 Dex Save + 15 Dex Save
+0 Wis Save +22.31 damage per day +42.00 damage per day +39.81 damage per day +15.75 damage per day
+5 Wis Save +15.75 damage per day +29.65 damage per day + 28.10 damage per day +11.12 damage per day
+10 Wis Save +9.19 damage per day +17.29 damage per day +16.39 damage per day +6.49 damage per day
+15 Wis Save +2.62 damage per day +4.94 damage per day +4.68 damage per day +1.85 damage per day

If we are spending enough days, it is always worth it, and you can find out if it's worth it by multiplying the bonus we get by the number of extra days, and comparing it to the loss from the first two days (I'll show some examples later).

Slow

Slow is only worth it if you are going to be preparing for an extended period of time. Here is the adjustment table for the first two days:

+0 Dex Save +5 Dex Save +10 Dex Save + 15 Dex Save
+0 Wis Save -6.45 damage per day -3.35 damage per day -0.26 damage per day +2.84 damage per day
+5 Wis Save -11.28 damage per day -8.19 damage per day -5.10 damage per day -2.00 damage per day
+10 Wis Save -16.12 damage per day -13.03 damage per day -9.93 damage per day -6.84 damage per day
+15 Wis Save -20.96 damage per day -17.87 damage per day -14.77 damage per day -11.68 damage per day

...and here are the damage adjustment tables for the proceeding pairs of days (notice the exact Dexterity save doesn't matter since it is a flat reduction):

+0 Wis Save +17.50 damage per day
+5 Wis Save +12.35 damage per day
+10 Wis Save +7.21 damage per day
+15 Wis Save +2.06 damage per day

Examples

One big elephant in the room, however, is that with damages of this calibur, most of our targets will have Magic Resistance. This makes bestow curse all the more valuable to cancel out that advantage the targets would normally get on the saving throws.

For these examples, I'll just be doubling the amount of runes needed to account for this advantage, because the extra spreadsheet math would take quite some time (and I've already done a lot to get this far).

The procedure has gotten a bit complicated at this point, so I am going to show three examples. I have chosen the Tarrasque (for something with a lot of HP but not all that great of saves), Zariel (for some realy good saves) and an ancient red dragon (for a middle ground).

Note: for the sake of comparison I am granting this ancient red dragon advantage on saving throws too.

The Tarrasque

The Tarrasque has the following relevant stats:

  • 676 HP
  • +0 Dexterity save
  • +9 Wisdom save

First let's see if bestow curse and slow are worth it:

Let's estimate our Tarrasque at +10 Wisdom so we can use are tables from above.

  • For bestow curse, we lose 28.52 damage on the first two days, but gain 9.19 for each day after meaning it is worth it if we need to spend more than 3 days on making runes.
  • For slow, we lose 32.24 damage on the first two days, but gain 7.21 for each day after meaning it is worth it if we need to spend more than 4 days on making runes.

Since the tarrasque has 676 hit points, and our runes accumulate 380.87 damage per day, we are covered after just 4 days accounting for Magic Resistance. Therfore, we do want to incorporate bestow curse, but not slow.

We spend our four days making 51 Explosive Runes and 1 Spell Glyph alongside our simulacra and after one big non-fire explosion, the Tarrasque is defeated.

An Ancient Red Dragon affected by foresight

An ancient red dragon has the following relevant stats:

  • 546 HP
  • +7 Dexterity save
  • +9 Wisdom save

First let's see if bestow curse and slow are worth it:

Let's estimate our dragon at +5 Dexterity and +10 Wisdom so we can use are tables from above.

  • For bestow curse, we lose 7.10 damage on the first two days, but gain 17.29 for each day after meaning it is worth it if we need to spend more than 2 days on making runes.
  • For slow, we lose 26.06 damage on the first two days, but gain 7.21 for each day after meaning it is worth it if we need to spend more than 3 days on making runes.

Since the dragon has 546 hit points, and our runes accumulate 329.40 damage per day, we are covered after just 4 days accounting for Magic Resistance. Therefore, we want to incorporate bestow curse and slow.

We spend our four days making 50 Explosive Runes and 2 Spell Glyph alongside our simulacra and after one big... also non-fire explosion, the dragon is slain.

Zariel, Ruler of Avernus

Zariel has the following relevant stats:

  • 580 HP
  • +7 Dexterity save
  • +16 Wisdom save

First let's see if bestow curse and slow are worth it:

Let's estimate Zariel at +5 Dexterity and +15 Wisdom so we can use are tables from above.

  • For bestow curse, we lose 30.32 damage on the first two days, but gain 4.94 for each day after meaning it is worth it if we need to spend more than 6 days on making runes.
  • For slow, we lose 35.74 damage on the first two days, but gain 2.06 for each day after meaning it is worth it if we need to spend more than 17 days on making runes.

Since Zariel has 580 hit points, and our runes accumulate 329.40 damage per day, we are covered after just 4 days accounting for Magic Resistance. Therefore, we do not want to incorporate bestow curse nor slow.

We spend our four days making 52 Explosive Runes alongside our simulacra and after a we never get to use fire explosion, Zariel is gone.

In conclusion

By using simulacrum every other day, you can accumulate quite a bit of Explosive Runes in a very short amount of time. Typically you are better off just making tons of runes, but occasionally Spell Glyphs like bestow curse and slow may be worth it.

Just about everything you would be up against can be taken out with 4 days of preparation. That being said, it will cost you a pretty penny since simulacrum and glyph of warding both have expensive components. All in all it will cost about 6900 gp per day if you follow my steps.

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    \$\begingroup\$ I suspect that within a week, I shall nom this Q&A for entry into our cheese hall of fame. 😊 Your thoroughness is to be commended. \$\endgroup\$ Aug 13 at 2:31
  • \$\begingroup\$ Fantastically detailed, thank you. Also for thinking of arcane recovery. One question, why you do not take a short rest on the first day (when you cast simulacrum) to recover a slot there, and why only a 4th level slot recovery, not a 5th level (which would give you an extra d8)? \$\endgroup\$ Aug 13 at 2:50
  • \$\begingroup\$ @GroodytheHobgoblin In the first day we run out of hours. 12 for simulacrum, 4 for glyphs, 8 for a long rest. We get 8 levels of spell slots from Arcane Recovery. two 4th level slots gives the same damage as one 3rd and one 5th. Either way works and has the same expected damage. \$\endgroup\$ Aug 14 at 13:41
  • \$\begingroup\$ @DavidCoffron Arcane Reovery is capped at level 5, you cannot recall spell levels of 6th or higher with it. (And I guess, the Simulacrum also cannot use it, as it cannot recoup lost resources, but I think you are not using that). The first day time limit: got it. \$\endgroup\$ Aug 14 at 19:06
  • \$\begingroup\$ @GroodytheHobgoblin right. You get 8 levels of spells to split behind 5th level or lower slots. 2 4th level slots is valid \$\endgroup\$ Aug 14 at 20:18
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74d8, or up to 592 damage per day of preparation

The most damaging way of using a glyph is to store a powerful spell with it. However, it comes at the cost of an additional spell slot. Because of that, for overall damage, it is better to stack the "explosive runes" variant of the spell :

Explosive Runes. When triggered, the glyph erupts with magical energy in a 20-foot-radius sphere centered on the glyph. The sphere spreads around corners. Each creature in the area must make a Dexterity saving throw. A creature takes 5d8 acid, cold, fire, lightning, or thunder damage on a failed saving throw (your choice when you create the glyph), or half as much damage on a successful one.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage of an explosive runes glyph increases by 1d8 for each slot level above 3rd.

As a 15th level wizard, we can cast the follow glyphs each day :

  • Level 3, 3 times -> 3 times 5d8
  • Level 4, 3 times -> 3 times 6d8
  • Level 5, 2 times -> 2 times 7d8
  • Level 6, 1 time -> 8d8
  • Level 7, 1 time -> 9d8
  • Level 8, 1 time -> 10d8

Assuming the target fails all their saving rolls, the full damage would be 74d8, or a maximum possible damage of 592. If we need to use our 8th spell slot to access the Demiplane, the damage goes down to 64d8, or 512 maximum possible damage. Feel free to mix up the damage types and in just a few days of intense casting you get a fancy firework of death that can kill just about anything.

(thanks to Groody for the following stats) If we take into account an expected fail rate on Dex saves of 60%, the average damage would be of 266 with the 8th level spell slot, or 230 without.

Can you really stack glyphs though?

For the glyphs themselves, nothing in the rules mentions that you cannot overlap them on the same surface, so there shouldn't be an upper limit of how many glyphs we can fit in our demiplane.

For the effects stacking in a single round, this question treats the subject of stacking the effects of instantaneous spells and whether or not they can stack at the same time. The great majority of people seem to agree on the fact that fireballs can stack with each others, so since the explosive runes work the exact same way it seems logical to assume that all the damage can stack in a single round.

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  • \$\begingroup\$ Not part of the question so just added info tidbit: at an expected 60% fail rate on Dex saves, the expected average damage delivered for this would be 266 points per creature hit. 230 if you use a Demiplane, as you have to use your level 8 slot to re-summon it to execute the ploy. \$\endgroup\$ Aug 12 at 7:50
  • \$\begingroup\$ @GroodytheHobgoblin you're absolutely right, thanks! I'll correct this right away. \$\endgroup\$
    – Matthieu
    Aug 12 at 7:53
  • \$\begingroup\$ At max damage, it would not quite kill or Zariel, Tiamat, or the Tarrasque (there are also immunities of course). At expected damage, ancient dragons, dragon turtles, pit fiends, and a bunch of demon lords survive it (even without considering magic resistance) and the odd other high-end monster like a marut. But it seems pretty save that with 2-3 days of prep, and 4,400-6,600 gp, you could kill pretty much anything in the game with this, and as you say, even with one day, nearly anything. \$\endgroup\$ Aug 12 at 8:03

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