Does the effect of the spell Entangling Staff deal varying constriction damage dice based on weapon size?

Question

The spell Entangling Staff (Spell Compendium p.83) causes the caster's quarterstaff to grow vines and constrict opponents. The relevant section reads:

If your grapple check succeeds, your quarterstaff's vines that can constrict one's foe, dealing 2d6 points of damage

Normally, constriction damage changes with size just like other natural weapons. I am unsure how it would play out in this case, though. For example, if a large hill giant druid uses this against a player via his large quarterstaff, would the constriction damage be 3d6, or would it stay at 2d6 no matter the size of the caster/quarterstaff being used?

Answer 1

The damage does not scale with size.

The constriction damage does not scale with the size of the quarterstaff because the quarterstaff is not what is constricting the opponent.

Look at the descriptive/flavor text of the spell. In this instance, it is actually important:

Rapping your staff with a knuckle, you cause it to sprout wriggling vines that grab and lash at the air.

Then this line in the rules text quoted in the original question:

If your grapple check succeeds, your quarterstaff's vines constrict your foe, dealing 2d6 points of damage . . .

Ultimately, the quarterstaff is not constricting anything -- "your quarterstaff's vines constrict", which are simply an effect created by the spell irrespective of the quarterstaff's size. If the quarterstaff was constricting as if it were some kind of animated object, then the damage would follow the rules for constricting which includes adjustment based on the size of the constricting entity where listed damages typically refer to the assumed default size for a creature, but that simply is not the case for this spell.

Answer 2

No scaling

Spells only do what they say they do, the rest is a houserule. This spell says that damage is 2d6, so that's what it is. Some spells take size into account (for example Shillelagh - damage dice as if two categories larger), some do not (Mage’s Sword damage 4d6+3).

Spell you are asking about does not say anything about the caster or weapon size, so the size is irrelevant. Allowing change in damage dice would be kinda similar to giving bigger dice when someone casts Magic Missile, or Magic Stone. I agree, it would make sense that hurling larger stones as Magic Stone would deal more damage, but the spell says 1d6+1 points of damage, so that's it. Not even Str bonus included.

But

It looks like you are building an NPC, and NPC does not need to follow each and every rule meant for PC. If it makes sense and would make the story more interesting, then yes, DM is allowed to decide that it scales. Just remember that these spells will be overpowered for their spell levels, and thus encounter will be more difficult than encounter calculators say.