Sure. What exactly are your criteria? - area effect, an actual physical projectile and damage measured in d6s (for some reason) are what I'm getting from the OP.
Here's a few of those. If your criteria are different than I'm reading, let me know.
Gourd of Fire Burping
What exactly are your criteria? - area effect, an actual physical projectile and damage measured in d6s (for some reason) are what I'm getting from the OP.
Basically as much damage as possible without resorting to a retributive strike from a Staff of the Magi or Power. Basically looking for something a non-caster like my Bard could use to do as much single-shot damage to a BBG as possible. Area effect not necessary, so could be cone or line of effect.
Use Magical Device is a possibility.
Elixir of Dragon Breath is a good suggestion, thank you. However a 10d6 gem from the necklace of fireballs is obviously a little more potent. Although the Elixir has a higher save DC so it could theoretically deal more damage.
|Darigaaz the Igniter|
Single target? That's easier. You can avoid paying the premium for area effects too.
With the use of UMD - a simple CL 11 scroll of Scorching Ray (or Admonishing Ray) is 12d6 damage for 550 GP. But maybe you don't want ranged attacks for whatever reason. If you want a melee attack a CL 10 scroll of Intensified Shocking Grasp is 10d6 for 500 GP.
If you want something which avoids attack rolls entirely then a Greater Aggressive Thundercloud (or Greater Flaming Sphere) scroll costs 700 GP and does 6d6 per round, DC 16 Reflex negates. If the enemy is inclined to attack you then Caustic Blood (at least CL 7, druid list or at least at least CL10 off the summoner list if you don't want another UMD check for the Wis required) does CLd6 acid Reflex half (+Reflex negtes for half as much on the next round) for each slashing or piercing attack which hits you. This is how to kill TWFers fast.
Along the lines of Darigaaz's idea, there's the sheaf of Explosive Runes/area Dispel Magic option.