How would you aducate this anti-dragon tactic?

[azmodean]

Situation: medium-level party travelling outdoors, they see a dragon at distance (probably at least 500'), the key here is they arenot suprised.
Magic user readies to cast wall of force right in front of the dragon when it reaches a specified distance.

Wall of Force
Evocation [Force]
Level: Sor/Wiz 5
Components: V, S, M
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft./2 levels)
Effect: Wall whose area is up to one 10-ft. square/level
Duration: 1 round /level (D)
Saving Throw: None
Spell Resistance: No
A wall of force spell creates an invisible wall of force. The wall cannot move, it is immune to damage of all kinds, and it is unaffected by most spells, including dispel magic. However, disintegrate immediately destroys it, as does a rod of cancellation, a sphere of annihilation, or a mage's disjunction spell. Breath weapons and spells cannot pass through the wall in either direction, although dimension door, teleport, and similar effects can bypass the barrier. It blocks ethereal creatures as well as material ones (though ethereal creatures can usually get around the wall by floating under or over it through material floors and ceilings). Gaze attacks can operate through a wall of force.
The caster can form the wall into a flat, vertical plane whose area is up to one 10- foot square per level. The wall must be continuous and unbroken when formed. If its surface is broken by any object or creature, the spell fails.
Wall of force can be made permanent with a permanency spell.
Material Component: A pinch of powder made from a clear gem

Assumptions:
Dragon is moving at high speed (100' to 300' per round).
Dragon's manuverability is Poor.
Dragon may or may not see wall of force (results of both eventualities would be nice)
caster can place the wall of force in front of, but not touching the dragon.
caster can react fast enough to cast the spell once the dragon is within 45' of the caster (the minimum range of the spell)
Wall is at least 30'x30' and centered in front of the dragon.

Quetions:
Is there any chance of the dragon avoiding the wall completely?
If the dragon hits the wall, how much damage would it do? (as per falling damage?)
is there any chance of the dragon reducing the damage?

 

[KarinsDad]

A few thoughts on this:

1) The breath weapon for most Dragons is more than 45 feet. Chances are that at least some of the PCs, possibly even the Wizard, will be damaged before the Dragon gets into range.

2) If the Dragon is moving 300 feet per round, it is moving 50 feet per second (in a 6 second round). This is effectively the same speed as a falling body after 2 seconds (i.e. 32 feet per sec^2 = 16 feet per second after one second and 48 feet per second after two seconds). The distance that someone falls after falling 2 seconds is 64 feet (dist = 1/2 a*t*t = 16 * 4 = 64 feet). So, the Dragon would take 6D6 of damage from hitting the Wall of Force, but the damage reduction of the Dragon would stop some of that.

Although not totally accurate, a rough rule of thumb you could use is 1D6 damage for every 50 feet per round a creature is moving.

3) I would not really give the Dragon a chance to avoid the wall. The wall is just too big. It is a fifth level spell after all, doing the damage of a second level spell.

However, a different DM might rule that a Dragon with the Hover feat could use a move action to stop dead in his tracks, Hover, and avoid the wall. But at minimum, I would have the Dragon attempt a Spot check to see a non-moving Invisible object which has a DC of 40.

And, he could only do a Spot and Hover if the Wizard cast this spell on his normal turn. If the Wizard cast the spell as a Ready Action (i.e. when the Dragon gets within 40 feet of me, ...), then the Dragon is in the middle of his movement and would not get the Spot roll.

 

[smetzger]

Assumptions:
Dragon is moving at high speed (100' to 300' per round).
Dragon's manuverability is Poor.
Dragon may or may not see wall of force (results of both eventualities would be nice)
caster can place the wall of force in front of, but not touching the dragon.
caster can react fast enough to cast the spell once the dragon is within 45' of the caster (the minimum range of the spell)
Wall is at least 30'x30' and centered in front of the dragon.

Quetions:
Is there any chance of the dragon avoiding the wall completely?

My reading of Blindsense is that it won't work in this situation. But the standard Spot DC of 20 or if the Dragon has see invisible up will work.

If the dragon hits the wall, how much damage would it do? (as per falling damage?)

edited...Oops bad math KD is right. 6d6 damage.

is there any chance of the dragon reducing the damage?

I think DR applies here.

So, most likely it will delay the dragon for a round or two, and embarass it and make it angry.

 

[Altamont Ravenard]

I think the Dragon would notice/see the wall, per Blindsight. I don't think he'd be able to avoid it, if the Wizard readies an action to cast the spell right in front of a fast-moving Dragon, unless you let the Dragon make a Spellcraft check. If the check is made, the Dragon could guess that the Wizard is trying to block his path, and stop before said Wizard finishes casting the spell.

Damage sounds about right. The dragon would indeed be angry, and would want to kill the party, especially the wizard (concentrate all attacks on him), but a smart dragon would use the Wall to its advantage.

AR

 

[Derren]

Depending on how you see Wall of Force blindsense might or might not work.

If you think of a WoF as a solid, but invisible wall, then blindsight would work and a crash would do damage. If you think WoF is only a force which prevents anything from entering the space then blindsense would not work, but the dragon would get no damage as there is nothing solid to hit.

Also it depends when the WoF is casted. When the dragon still has a standard or movement action left, hovering or casting a spell is no problem to avoid the wall. If the dragon has no action left he hits the wall, possibly for 6w6 damage (If flying 300 ft. a speed which is very high even for dragons)

 

[Mordane76]

As long as the spell has V,S components, the dragon should get a Spellcraft check (since, IIRC, dragons have Spellcraft as a class skill, and most should have ranks in in). Without Hover, however, the dragon can't really do much due to its maneuverability. The dragon, if it has a move action left, might be able to slow itself by whatever it is allowed per Poor maneuverability, and thus take less damage.

The damage, IMO, is caused by the impact, not the spell, and thus is not a magical effect for bypassing DR - its DR should apply, if it has any.

 

[Ogrork the Mighty]

We had this exact situation come up in our game. The dragon got a Reflex save for 1/2 damage; I think we ruled 10d6 due to its speed.

I would think blindsight would work. If a bat can see it, I would think a dragon could too.

 

[was]

Well, dragons are highly intellegent and magical creatures with innate spell casting abilities. It might be able to sense/see a spell being cast and attempt to identify it via a spellcraft check or sense the location of the magical creation even if it cannot identify exactly what it is.

 

[azmodean]

I had forgotten about both spellcraft and blindsense.
Also the low damage seems to make this a pretty pointless tactic unless you have some kind of follow-up in mind. (I hadn't whipped out the acceleration formulas, I was assuming 300'/rd would do a lot more damage than that) On the other hand, it does let you get through SR, and possibly a save, depending on your interpretation.

 

[KarinsDad]

On the blindsense issue, Dragons have blindsense, not blindsight. This does not make much of a difference except that the Wall of Force has total concealment against the dragon and hence, the dragon has a 50% miss chance against it.

Only kidding.


What this means is that the Dragon can sense the wall at the last possible instance, but not see it.

The other aspect of this is that most of the time, the only way to get this tactic to work is for the Wizard to have a Readied Action to do it.

This basically negates Spellcraft for the Dragon, etc. with respect to avoiding the wall. By the time the Dragon notices the spell casting, it is too late (rules-wise) and the wall is too big to avoid. The DM might allow the Dragon to get off a Quickened Dispel Magic (to counterspell) or Quickened Dimension Door (or some such) if he makes his Spellcraft roll, but most Dragons will not have that available. Most Dragons will have no options and crash into the wall, even if they make their Spellcraft to notice what the Wizard cast.

An evil DM might allow the Dragon a reflex saving throw to disrupt the spell completely (i.e. "The wall must be continuous and unbroken when formed. If its surface is broken by any object or creature, the spell fails.").

Mostly, this tactic will just tick off the Dragon and he will Hover behind the Wall of Force from one half of the battlefield for the cover bonus (improved +8 cover if only his head sticks out) and use his breath weapon to devastate the party.