area effect spells and large creatures

[Kershek]

For area effect spells, do you have to hit the whole creature in order for it to be affected? For instance, if I hit the corner square of a 15x15 huge monstrous spider with a glitterdust spell, is it affected?

 

[Crothian]

I'd rule you'd have to at least hit it's face fopr the blindness part. If it was invisible, that part of the creature would have glitter dust on it.

 

[Kershek]

But there's no facing in 3E...

 

[LokiDR]

From a rules stand, the glitterdust works if the creature is in the area. As for facing, apply some logic.

Player: I glitterdust at ground level 20' east
DM: Congrats, you have outlined a dragon's foot.

If it isn't that simple, like a huge displacer beast, make a DM call. Does it make sense that it's eyes were in the area of effect? If you are affecting what would be the opposite "side" of the thing from the direction of the person it is attacking.

If you don't like any of those, just figure out what percentage of the creature is affected, and roll it. If you make the roll, then the creature is subect, else not.