1) Casting a spell -line of sight/line of effect: I find the PHB to be a bit confusing about this. On the one hand it says that I have to specify one corner of a square, so I would have to see the point and aim at it. But then it says that its enough for spells like summon monster to just be specified in some way. The difference in both is if you can cast a spell (lets say fireball) into an area that you can't see, like darkness or a fog cloud.
So, do I NEED line of sight or is line of effect sufficient for a fireball?
Whether you need line of sight or line of effect (or neither) depends on the spell being cast. Since you mentioned "one corner of a square", we'll start with area effect spells like fireball and fog cloud. For these you need line of effect. Doesn't matter if you can see it or not. If for some reason, the area you choose can't be reached (eg, wall in the way), the spell fizzles. Fireball is an exception to the fizzling, because the spell description trumps the normal rule, and the spell says
You point your finger and determine
the range (distance and height) at which
the fireball is to burst. A glowing, pea-sized
bead streaks from the pointing digit and,
unless it impacts upon a material body or
solid barrier prior to attaining the
prescribed range, blossoms into the fireball
at that point. (An early impact results in an
early detonation.)
Summoning monster requires that the creature has a solid surface to appear on (it's not in the description, but it's written down somewhere). If you summon a bear "25 feet ahead", and don't know there's a cliff in 20 feet so the bear would appear in mid-air, the spell fizzles and nothing is summoned - but the spell is still used up.
Spells that require line of sight are usually the spells where you have to pick and choose who's being affected - eg, magic missile, charm person, finger of death. Being able to touch the creature is as good as seeing it, if you can't see for some reason.
[/quote]We had a bit of confusion yesterday, as a monster was inside a fog cloud and we wanted to shoot ray attacks blindly into the square the beast was supposed to be. Reading up on it later, I am sure that rays are to be handled like ranged attacks with a bow. But a fireball doesnt work like that, its not "thrown" like a missile, it actually emminates from one spot.[/quote]
You can shoot ray attacks blindly, but like trying to hit an invisible creature, it's considered to have "total concealment", which means you have a 50% miss chance. That's assuming you're shooting at the square it's actually in; if it's in a different square, you just plain miss. A fireball doesn't care - it hits if the creature's in the square, or within the area of effect (eg 2 squares over).
2) Do cloud effects stack? Lets say I cast a 2nd acid cloud inside of another acid cloud. Does that work or does it just replace the previous cloud?
I'm not sure. I would think the acid damage stacks, but the other parts don't (slow movement, penalty to hit)
3) Touch attacks as attack action? The wiz uses a touch spell and tries to touch a target. The first time he does this he uses his action to cast the spell including the touch attack. Lets say he misses , then the spell is still charged. In the next turn he would have 2 attack actions (thanks to fighter lv and total Lv) can he now make 2 touch attack -attempts (or until discharged) ?
I would say yes, as the casting of the spell is what stops you from doing it multiple times in the first round. Equally, touch attacks as AOOs (the spell was cast before but is not discharged)?
Assuming the touch attack is discharged on a successful hit, then I think you have it exactly right. One attack the round you cast the spell. Multiple attacks the following rounds, until you finally hit. You can use it as an AOO assuming the spell was cast earlier and not dispelled.
If the touch attack allows multiple touches (eg Chill Touch), then it gets confusing. We just had a discussing about it on another thread, and I was left feeling like the rules didn't cover the situation well.
Good luck!