Quote from Eskil >>

Does "The spell's base damage is 12d6. If at the end of your turn the bead has not yet detonated, the damage increases by 1d6." mean that the max damage is 22d6? that seems very high

 If you don't add any modifiers to it, then yeah, that's the highest damage you can get by charging the spell. As has been discussed elsewhere in the comments, though, you can use an Extended Spell metamagic modifier to double the possible charging time, resulting in a new possible max of 32d6 damage after 2 minutes of charging (not 24 hours, as someone speculated -- while Extended has a maximum time limit of a full day, that only means that trying to double the time limit of a 16-hour spell would only go up to 24 hours).

Personally, I'm inclined to give this to my Order of Scribes wizard, let him mess around with the damage type, and turn the attack into a delayed-activation 12d6 bludgeoning sucker punch by an invisible magic giant.

Or be an evocation wizard, just no damage at all

say i cast this spell, put it into a piece of bread. it doesn't "strike" the bread, so the explosion doesn't occur; someone else eats the bread. you run away and stop concentrating. they freaking EXPLODE like a human bomb. this spell is insanity.

Quote from Lorn20 >>

So years ago my DM created an encounter specifically so she could cast this spell. Unfortunately they forgot that the magic item they game just before the encounter me gave fire immunity rather than fire resistance as they thought it did. So we had an amusing 10-60 minute discussion (on and off, it was years ago some details are fuzzy) about what would happen if my fire immune 6-intelegence half orc barbarian just ATE the Delayed Blast Fireball. And I mean that quite literally, grab it, throw it in my mouth, and try to swallow before it exploded. We were going back and forth on the "rules as written" answer of either I take no damage or my mouth gives the fireball directionality or I take some amount of force damage as the fireball tries to expand but only encounters non-flammable material in a space much smaller than a 20-foot-radius. Ultimately we decided I wouldn't do that to save us the head ache of "WTH happens?" But I am curious what other people think would happen. (This character was a bit silly so doing this would 100% be in character, possibly even with only damage resistance)

If you want my 2 cents, there's a specific phrase in the spell that'll give you the answer.

• When the spell ends, either because your concentration is broken or because you decide to end it, the bead blossoms with a low roar into an explosion of flame that spreads around corners.

I would say it depends on if your fireproof barbarian opens their mouth. If they open their mouth, then everyone in the 20 ft radius gets affected normally. If they close their mouth, nothing happens. There's nothing in the spell that says anything about force damage. I understand that normally explosions have a shockwave, but Fireball isn't really a traditional explosion. It's just a magical ball of fire. If it were a traditional explosion, creatures immune to fire would take SOME damage.

what would happen if you replaced a pearl from in a ring with it? Would it go off if you touched someone with that hand?

"person you don't like! It's so good to see you!"

go in for a high-five or a handshake

with some form of dodge ability, just blame it on spontaneous combustion.

Trap an enemy in a Forcecage with an Iron Golem and a few Delayed Blast Fireballs and you get a meat grinder.

Quote from Alethalion >>

14d6 using 9th level spell slot + 9d6 for 9/10ths of the duration. 23d6, and x2 damage with vulnerabilities to fire. uhh i just rolled 164damage. 

 14d6 with 9th level + 10d6 for duration. Bonus action extended spell at the end of round 10 for an extra two minutes if you interpret extended spell as resetting the duration for +20d6, or an extra 10d6 if not. Then x2 for vulnerability and thats 88d6 or 68d6 fire damage. Other party member cast Hold Person or Hold Monster, then rinse and repeat.

Any sorcerers out here who’ve used extended spell metamagic on this?

Could you cast Time Stop then cast this spell and let it cook until the stop is over then release it for a lot of damage?

Quote from luigiguy0987 >>

Any sorcerers out here who’ve used extended spell metamagic on this?

 Just check the comments on pages 1 and 2