I’ve been witness to a bunch of heated arguments about how stacking the same weapon enchantment on the same weapon works. There are clear sides in this battle for and against it. I used to be in the “sure, why not” camp, but I find myself squarely on the “nope, it won’t work” side now.
Here’s my attempt to put this argument to bed.
Why Won’t It Work?
When you enchant a weapon, you don’t “give it more damage”, you give it a quality. This quality is the enchantment that you specify: flaming, shocking burst, brilliant energy, etc.
Once a weapon has that quality, it has it. That’s it. You couldn’t make a brilliant energy weapon “more” brilliant energy because it already is a weapon with that quality. This is obviously one of the easier-to-visualize examples.
The same thing applies for all qualities that grant extra damage. It’s the quality that grants that damage, you’re not just “giving more damage to the weapon”. And since a weapon either is or is not a particular quality (there’s no way to be “half flaming” or “partially brilliant energy”), you can’t “double up” a particular quality and expect it to give double the benefit.
You can always make up your own weapon abilities that give double the benefit of an already made ability, but some may not be balanced at a +2 ability and should be carefully examined before simply assuming it can or should be done.
A Word On Stacking
I want to include some text from the SRD that also supports the “they don’t stack” point of view:
In most cases, modifiers to a given check or roll stack (combine for a cumulative effect) if they come from different sources and have different types (or no type at all), but do not stack if they have the same type or come from the same source (such as the same spell cast twice in succession). If the modifiers to a particular roll do not stack, only the best bonus and worst penalty applies.
In the case of our +1 flaming, flaming, flaming longsword, since the three separate +1d6 points of fire damage all come from the same source (the flaming weapon ability) then they should not stack with each other to the damage roll.
This all supports my initial argument.
One Quick Point On Creating This Weapon
Everything that I’ve outlined thus far basically talks about how the same abilities interact when placed on one weapon. This obviously makes the assumption that you were able to create this weapon in the first place. The reality of the situation is that you can create a +1 flaming, flaming, flaming longsword, but the bonus to the damage roll will only have +1d6 flaming damage since the other 2d6 does not stack with damage from the same source (flaming damage from the same weapon).
So at the end of the day, you can make a sword like this, but it’d be a large waste of money and it won’t have the effect you’re hoping for. For this reason, I just take the natural next step and say that you shouldn’t be able to make an item like this (but if a PC really wanted to and was fully aware of the fact that it’d still only give +1d6 extra damage, I wouldn’t put up a fight).
Overspecialize & Breed In Weakness
While we’re arguing whether or not you can do something, we should also ask ourselves if there’s even a need or benefit to doing it.
Let’s take our +1 flaming, flaming, flaming longsword as an example. Assuming that the multiple flaming abilities stacked, that will add +3d6 (3 to 18, with an average of 10.5) points of fire damage to our attacks. That’s not too shabby. But what if someone has energy resistance to fire?
That’s 30,000gp worth of magical enchantments that’s been potentially eliminated by a 3rd level wizard and certainly by a 7th level wizard that casts that very common and regularly utilized spell.
If you had a +1 flaming, frost, acidic longsword, you still can net +2d6 points of alternate energy damage despite the loss of the flaming damage – and it’s questionable whether or not someone would even bother to ‘waste’ a standard action to avoid 1d6 points of damage when they could possibly use more effective defensive or offensive spells.
Ok, I Believe You, But It Doesn’t Sound That Bad
You know, you’re right in some ways. As long as we acknowledge that the current rules do not allow this stacking and that doing so is a house rule, I don’t see any intrinsic problems with allowing it – as long as we take a close look at anything proposed and be sure that balance is maintained.
First, I’d only allow the stacking of energy-based weapon abilities. These are the flaming, frost, acid, etc. abilities. Since you can already mix and match different energy types on one weapon, there are very few situations in which you’d gain a benefit from all of that energy being from the same type. In most cases, you’re at more of a disadvantage (as mentioned above) than not. The only clear advantage you’d get is if you were battling something that had a listed vulnerability of the damage type your weapon did.
Second, for any other weapon ability, you need to take a close look at the effect and it’s potential for abuse. Let’s take a crazy example: +1 4x(wounding) longsword (a +9 equivalent weapon). Remember that the wounding ability does not offer a save – the target automatically loses a point of Con for each successful hit. This would mean the majority of creatures would die in a single round when being attacked by most mid to high level fighter types.
Would I pay 162,000gp for a +1 4x(wounding) longsword? Hell yeah! Any fighter would be insane not to consider this unless they constantly fought creatures that were immune to critical hits.
The best approach to this will be to create a single modified weapon ability that combines all of the abilities that you wish to include. For our original example, we’d have a +1 Triple Flaming longsword where the Triple Flaming ability just adds +3d6 fire damage to a successful hit. Handling things this way will reach a balance between allowing the stacking of similar weapon abilities and eliminating abuse through upgrading their magical items.
The most important thing, however, is taking a solid look at what they want to do and making sure that if it’s overly powerful that you adjust the bonus of the ability to reflect its power. My +1 4x(wounding) longsword should never happen, for instance.
DMs just need to be careful with what they do and don’t allow. The enchantment system was obviously not intended to be used like this and there’s some serious potential for abuse and brokenness if you allow everything blindly.