Question about interactions with incorporeal creatures.

[Toshy]

I have run some encounter where my players were facing incorporeal enemies, but might have made some mistakes regarding their bodyless nature.

I re-read the incorporeal extraordinary ability again and want to make sure I've got everything right.

Please correct me if I got something of the following wrong:

1) An incorporeal creature is immune to any non-magical attack.

2) Spells and magical attacks deal only 50% damage.

3) Spells from a corporeal source and effects that deal no damage, have only a 50% chance to work at all.

Does this include damaging spells as well? If so they would be considerably worse than physical magical attacks?
Is it read as "spells - and effects that deal no damage" or as "spells and effects - that deal no damage"?
The question came up, as it mentions channel energy as an exception, which would be a damaging effect.
What would non-spell, non-damaging effects (that could affect an incorporeal creature) be at all?

4) Force Spells and effects ignore everything above.

5) Holy water is an exception to (1), as it would affect an incorporeal creature.
But would deal only half damage as per (2), correct?

Thanks in advance, I hope I wasn't handicapping my players to bad.

[Chuck Mount]

"3) Spells from a corporeal source and effects that deal no damage, have only a 50% chance to work at all.

Does this include damaging spells as well? If so they would be considerably worse than physical magical attacks? "

If a spell deals no damage (i.e. Slow or Web), have a 50% chance of working.
Just like it says for damaging spells, "Spells and magical attacks deal only 50% damage.", damaging spells do 1/2 damage.

[zza ni]

5. holy water effect incorporeal undead (or other incorporeal creatures that are effected by holy water) at 100%.
The part about holy water is separated from the rest and as each part before took the time to explain if it effect at full or part. since all that is said is "Although it is not a magical attack, holy water can affect incorporeal undead" without calling out any reduced effect, it mean it's effect is not reduced.

Same for channel energy.

As a side note, in my games this extend into ANY positive energy meant to deal damage to undead. So cure light wounds or disrupt undead gain the same benefit of 100% damage and no miss chance vs incorporeal undead. since it seem like a theme and I like to have a general rule instead of an expectation to each case. (I don't like saying 'positive energy in a vail of water or from a holy symbol works, but the one from a ray made with a spell doesn't, just because it wasn't mentioned')

[Azothath]

There are many more statements in the description than your list.
You are treating as a descending dependent list when they are descriptive statements grouped by paragraph(topic). If you put it into a logic tree it would have many branches.
I tend to think of it as a special state like gaseous but different.

0) A creature is corporeal XOR incorporeal.
Interactions between the two are governed by the description. It is assumed that if both are incorporeal then things carry on as usual (a spellcaster can not use material(aka corporeal) components when incorporeal).
Incorporeal creatures have a body. PCs can see it. It is just not "physical" in the common sense like being solid or gaseous. They can talk and be heard and have perception.

1) The first paragraph details common interactions & attacks. Mundane and mundane attacks, attacks with magic weapons and spells.
Holy Water and Channel Energy have full effect.
[Force] effects (it's a spell descriptor) means they have full effect. If it carries a condition then you'll have to see if it applies as incorporeal & undead have many immunities.

2) The second paragraph talks about AC.

3) The third talks about movement and perception.

4) The fourth paragraph talks about the incorporeal's attack upon a corporeal creature.

5) The fifth closes with more details about #3.

[Mysterious Stranger]

3) Spells from a corporeal source and effects that deal no damage, have only a 50% chance to work at all.

The phrase “that deal no damage” specifies the 50% chance to work only applies to non-damaging spells.

Force spells and effects, such as from a magic missile, affect an incorporeal creature normally.
This makes it clear that force effects basically ignore the incorporeal ability and affect the incorporeal creature as if it did not have the incorporeal special ability.