However, you absolutley, positively cannot simply declare a Touch Attack to do this - that's not allowed anywhere in the RAW and I see no reason to allow it.
The only rules language in the Touch Attack section is on calculating Touch AC. There are no attendant rules on what can and what cannot be used to deliver a touch attack. The rules are simply silent.
You can, of course, choose not to allow melee weapons to make touch attacks, but you can't really base that on RAW. That is
pure DM interpretation- I'm not saying its
invalid)- its just not based in rules (nor in the RW).
If this is the case, why does Flame Blade mention "A flame blade can ignite combustible materials such as parchment, straw, dry sticks, and cloth", but does not explicitly mention creatures, their hair, their clothes, their equipment, etc.?
Because by the very structure of the sentence, in the form of the phrase "combustible materials such as," you can see that it is not meant as an exhaustive list.
I opine that "exposed" means that you are "continuously exposed" (i.e. noninstantaneous) to these magical fire effects, not that you are quickly (i.e. with an attack) exposed. It seems unlikely that if the designers meant that these types of attacks could catch a creature on fire, that they never mentioned it in the pertinent spells / special abilities.
This is a fair reading, though I've never seen it played that way. But if you so interpret it, then you must rule similarly for exposure to torches used in melee combat to be consistent.
The problem with your side of the fence here is that all weapon damage occurs in the game on a successful hit. Hence, all Trip attacks do all weapon damage the moment the melee touch attack successfully occurs.
If you look at the other attacks in the special attack section (where trip et alia are located), they tell you if and when you deal damage- such as with grapple. Grapple has a damage dealing section, thus you deal damage with grapples when the rules say you do.
Trip has no such section saying that you can deal damage, thus it does not. I think we agree on that.
Where we disagree is whether, when there is no underlying damage, an energy weapon still deals its energy damage- hence the question about attacks like trip.
IMHO, energy damage is triggered on a successful hit, and does not require underlying damage. Its
sole prerequisite is a successful hit. It is unaffected by conditions that diminish, nullify or substitute other effects for the normal effects of a weapon strike.
In other words, when a weapon with an energy enchantment is used to deliver a successful strike, there is a conceptual bifurcation. Down one path is the normal damage and other effects of the weapon strike. Down the other is the damage delivered by the enchantment. The target is subject to both branches, but neither branch affects the results of the other.
And yes, this means that if you allow extra damage from special weapon abilities, then Vorpal Weapons could auto-kill an opponent with a melee touch attack Trip attempt, regardless of whether the opposed check is made or not because the opposed check is not the successful hit.
This is where you must use your mind instead of mindlessly following rules that produce inherently inconsistent results. Quite simply, RAW cannot solve all inconsistencies.
To trip someone, you must hit their legs, and in fact, you must declare you are making a trip attack before rolling- you are, in effect, making a called shot to the legs. To behead someone, you must hit the shoulders, neck or head. The Vorpal enchantment effectively guides a normal strike into that area...and, as I recall, only on a
critical hit.
Unless I'm mistaken, those body parts are generally at "opposite poles" from each other, so you have a logical impossibility. You have a conflict of rules of equal specificity.
OTOH, if this were a Sword of Sharpness, there is no inconsistency, since a limb is a valid target for a weapon with this enchantment.
If you have a Vorpal Guisarme or Whip that rolls well enough to trigger its special ability while doing a trip attack, you could rule that:
1) Because the person was aiming for a Trip attack, the Vorpal enchantment CANNOT trigger. (The Trip rules supercede the Vorpal enchantment rules.)
2) Because the person was aiming for a Trip attack, the Vorpal enchantment acts as normal if and only if the attack roll would hit the target's normal AC- which, since it requires a crit, it would. (The Vorpal enchantment rules supercede the Trip rules.)
3) Because the person was aiming for a Trip attack, the Vorpal enchantment acts as if it were a Sharpness enchantment, and severs a limb. (Compromise between rules of equal specificity.)
