I've got a dungeon coming up that will include archers shooting from murder holes and arrow slits.
I'd anticipate the party's sorcerer will want to launch fireballs so the detonate inside the enemy defences, but there aren't really any rules i'm aware of to determine if this is anything other than an automatic success...
Because it IS automatic success. Why shouldn't it be?
I'm leaning toward making it a touch attack against DC 18 (since they provide a +8 to ac) with a range increment of 20 ft. Any thoughts?
Similarly, any rules for throwing fireballs past the melee line for hitting the monsters only?
Here's the standard line that I wrote years ago which I give in response to fireball questions:
In 3E, when someone casts a spell, people are where they are. If you can see it and it's in range of the spell, you can target it and there's no chance of hitting something else unless the description of the spell specifically notes it. The bit in the Fireball description about, "passing through narrow areas," is a somewhat more exotic application of the spell than simply targeting someone on the other side of a crowded battlefield. Casting a spell so that it passes through a small hole is different than simply making it explode on someone's face (at least as far as Fireball is concerned), mostly since the intention is to have the spell detonate in an area you CAN'T really see. The bit of description about hitting things that may be intervening between the caster and the target has a lot more to do with things like Walls of Force and invisible creatures than it does for normal stone walls and creatures that you can see normally.
As I said, for purposes of targeting spells, attacks, etc. when your turn comes up, things ARE where they ARE and movement is irrelevant. With few exceptions (such as firing missiles at targets involved in melee, or opportunity attacks) their "movement"
during the current individuals turn is nil. Yes, this is a gross simplification, but it's the way the rules work. It's also a simplification that avoids having to resolve all kinds of annoying inconsistencies (such as lobbing fireballs or anything else past large intervening opponents who might otherwise be considered to be moving).
There is very seldom any chance of missing what you want to hit with a spell in the same way as you risk missing something with a fired arrow. What you want to hit with a spell - you hit. Where you want a spell effect to go - it goes. AFTER the spell gets to where you wanted it to go, or hits the person you wanted it to hit – THAT is when you generally start dealing with avoiding or diluting the effects by a last minute dodge, resisting the damage dealt, etc. which is reflected in the saving throw.
Note also that it is the CASTER who points in the direction he wants it to go and gives height and distance - NOT THE PLAYER. Where the player wants the spell centered, it's centered -
just like any other spell effect. There is no weaving or control in-flight of the detonation bead, and more importantly no such control is needed.
Now, a fireball is not, "drop a bomb on a dime," kind of targeting, but neither is it supposed to require any further special effort to target it - except as
specifically described. It is thus safe to assume that a spellcaster can point to what he can see with a reasonable degree of accuracy that SHOULD make it unnecessary for any DM to ADD ON targeting rules in normal combat. If that were not the case then the description of the spell would surely not be going to lengths to talk about targeting through arrow slits, but instead would concern itself AT LENGTH with targeting in NORMAL combat, getting it past large creatures or into melees.
The need to make a ranged touch attack to hit a narrow passage is fairly clearly NOT meant to apply to space between creatures on any normal battlefield. It says, "narrow passage" and then gives a specific example of a passage that is narrow in the form of an arrow slit. This extra step is for when you ARE attempting to, "drop a bomb on a dime," and a finer degree of control than is normal in combat is necessary.
The one other factor that makes fireball different from other spells is that it CAN detonate before it reaches its intended target point if there is anything in the way that it will impact upon. However, as noted that means things you CAN'T see, not things you CAN see.
As always, the right of a DM to use his own preferred interpretation and house rules should (but apparantly never can) go without saying. However, there isn’t a need to look beyond the rules for solutions here because there just isn't a problem to be solved, as such. It only becomes a problem when the DM starts making new assumptions about how the spell SHOULD work, rather than how it DOES work. I don't know what it is about Fireball but it's always seemed to invite DM's to complicate it even further than the RAW description of its function already does.
Note also that Fireball is a spread effect, not a burst effect. Any intervening creatures do not form a physical barrier to the effects any more than they would the targetting. If the caster can see his target point there is no need to roll to bypass intervening creatures or accurately place his targetting, especially above and beyond ANY OTHER SPELL. The spell reaches the target point and detonates in a spread from that point. The effect spreads
around everything in its area – not in a line of effect from the center point of the detonation. Even if a target has total cover it doesn't provide a save bonus from a spread effect like fireball. In fact, because it is a spread effect there is little reason to even retain a special case function like targetting THROUGH an arrow slit - but that's because it IS a special case. You don't even need to bother targetting THROUGH an arrow slit if the spread will affect creatures behind it (and it will) - In 3E you only need to target through an arrow slit if you need to hit creatures WAY behind it.
