Hey,
I've been on the Isle of Crypts and got the chaos serpent eye. After returning to Xenka, she says the same thing again (she sends me to the Isle of Crypts again), as I ask her about instructions. Now I've heard about the infamous bug with the Hierophant and the missing "sacrifice"-dialogue option. I never talked to the buggy ghost and didn't take the serpent staff up to now. As far as I can say I've played the game very carefully (especially to avoid this known bug). Is there a way out of this situation?

Did you just pick up the serpent staff then, and if so, did you make sure to pick it up 'correctly'?

You'll need to collect the other pieces of the serpent regalia if you don't have them yet. The earrings, ring, and amulet are given during the southern cities' storylines, but in addition to the staff, you also need the crown and the armor.

Hi,
I have everything except for the armor and the staff (I decided to let it in the cave until I need it).
But is it really a requirement for the "sacrifice"-dialogue to have all the parts first? That seems strange to me, as there is no hint that I need them at that moment in the game. Or did I miss something?

You do need to acquire the staff to set one of the flags that enables the sacrifice dialogue. I'm not 100% certain that the other two pieces (crown and armor) are part of that same flag-set, although I know that they are required for at least one stage of Xenka's questgiving, and it may be this one. Regardless, you definitely need the staff; just be sure to save before you pick it up so that you can try again if it isn't done "right".

I'm assuming that, by this point, you've dealt with the Banes, restored Gwenno, and generally taken care of everything else.

Yes, I've done all the other things. So I'll try to get the staff. Hopefully it'll work. Thank you for now. :)

Ok, I got the staff (I directly stood on the thing and took it) - but it's still the same problem: When I ask Xenka, she repeats her "Use the tooth that I have given thee! Seek the Dead on the Isle of Crypts" - is there another thing to do on the Isle of Crypts? I only got the chaos serpent eye.

You've spoken to both the Great Hierophant and the Chaos Hierophant? (The latter is not on the Isle of Crypts.)

I feel ashamed now... I completely missed the Hierophant on the Isle of Crypts (I just flipped through the books in the Isle of Crypts temple). After I've spoken to the Hierophant there the dialogue of Xenka is changed now (now she sends me to get the serpent staff). Thank you for your assistance. I hope to be able to finish the game now. :)

I'm sorry, but I have another question. I understand that I have to find the chaos hierophant now - so I went to Sethys and talked to him, but the guy doesn't want to show me the way -he is still talking about his lost key (I assume that's the one I found in the treasure room after the rat-caves - the one that opens the door to the winch). He talks about he has to stay here until the place is cleaned before "Master of Tolerance" returns.

You've presumably 'rescued' Mortegro by now, so that's out of the way.

IIRC you need to have/show something to prove that you're a friend before he'll be willing to show you the resting place of the Chaos Hierophant.

Yes, Mortegro has already been hit by the lightning. ;)
It's strange - when I was in the temple the last time (when I "rescued" Mortegro), Sethys didn't trust me - I got the key in the treasure room and returned to him, but his attitude didn't change. Now after I returned to him, he talks to me like a friend and tells me about his Master. I have no clue what item I could need to make him guide me to his master or in what way I have to "clean" the temple of tolerance. I've searched through many walkthroughs without finding the solution.
Is it possible to reach the chaos hierophant without Sethys?

If he's talking to you in a friendly fashion - giving the appearance of thinking you're a Chaos follower - then you should be set and the option should appear somewhere in one of his dialogue branches. I don't have a save anywhere near this point to go back and check, but if you're missing any relevant artifacts - the serpent regalia, the blackrock serpents, etc - this might be the time to go get them. It's also possible that you missed an item on the Isle of Crypts, though again I'm not able to double check on just what you can find there.

Ok, something really really stupid is the problem... my party was already full (I have Boyden with me)! Unfortunately, Sethys doesn't mention anything about that, he just doesn't join, repeating his words about the cleaning of the temple again and again... now after (Shamino accidentally freezed to death) he joined immediately...
Thank you for your help, you've been very kind. :)

The game is odd that way, yes - usually you'll get a dialogue warning, but at other times it just leaves you hanging. Good to know that you figured it out though!