Attacking a ethereal opponent

[Minosis]

Recently I was confronted by a ninja out of the CA with the feat that allows him to attack while ethereal. He gets to go ethereal as a swift action right at the bginning of his action. This in essence means that he is attacking whike invisible which allows him to use the sudden strike ability. This means that he is attacking for 6d6 damage. Fortunately my GM can't roll to save his life, biut I know that he'll be back. Here is my question.

What happens if I ready an action so that is the split second when he is visible I grapple him, now if he goes ethereal do istill have a hold of him? Is it a 50% chance to still have him grappled. If yes, is every attack while grappling at the same 50% miss chance?

Is there a spell that would add ghost touch to a weapon?

 

[Lord Pendragon]

What happens if I ready an action so that is the split second when he is visible I grapple him,

You'd get to try and grapple him, though it'd do you little good because...

now if he goes ethereal do istill have a hold of him? Is it a 50% chance to still have him grappled. If yes, is every attack while grappling at the same 50% miss chance?

No. When you go ethereal, you shift onto another plane. Unless you have the ability to go ethereal as well, there's no way to keep a hold of him when he goes ethereal.

There is a counter for this ability, though. Talk with the party wizard about Dimensional Anchor. Having the wizard ready an action to peg the guy with a Dimensional Anchor is extremely effective.

Is there a spell that would add ghost touch to a weapon?

I believe there's a cleric spell that does this, though I don't know the particulars off hand...

 

[CM]

Libris Mortis has ghost touch weapon as a 4th-level cleric spell.

 

[AuraSeer]

What happens if I ready an action so that is the split second when he is visible I grapple him, now if he goes ethereal do istill have a hold of him? Is it a 50% chance to still have him grappled. If yes, is every attack while grappling at the same 50% miss chance?

I don't think that works. You don't even get the 50% chance unless some special ability makes your "grappleness" into a magic weapon. Magic fang might arguably have that effect, but the RAW don't specifically say so; it'd require a rather liberal interpretation from the DM. The best case would be an ability that let you grapple as a [Force] effect, but AFAIK there is no such thing unless your DM invents it.

I don't have CAd, but you should check whether the shift power is a spell-like ability. If it is, you can interrupt it and prevent him from going ethereal in the first place. A spell-like power is subject to AoO, just like a spell, and can be spoiled if the user is damaged or distracted. Your best bet then would be to grapple, and hope he can't make the DC 20+ Concentration check. (Unfortunately, this does not apply if it's a Supernatural ability.)