itch.io

Okay, dealing with the zhogtk is I think the next step. If you have picked up the Tome from the study then you should have access to everything to get rid of zhogtk so you can explore freely. I'll put the steps in strikethrough... itch doesn't seem to have spoiler tags.

• When the zhogtk appears Avery should be able to read an entry in the Tome about it. This will have reference to a book that you can only find once Avery knows he is looking for it.
• The book is in the single bookshelf immediately above where Zhogtk appears.  A piece of paper will fall out of the book when you read it but is in a strange language.
  
• If you combine the Tome with the note you can translate the text and reveal a code. This will gain access to the basement.

I think this is where you have got to, I'll include the next few steps below on how to deal with Zhogtk just in case they are needed either later by you or anyone in future looking at this thread for help with the Zhogtk puzzle:

• There are some items required for the banishing spell - the Tome, coal, incense burner and lighter can all be found in the mansion before the zhogtk appears. Sulphur (in basement) smallage incense (in basement) Pnom book (above zhogtk appearance area) can only be collected after Zhogtk appears.
• The "place of power" to perform the spell is in the old basement with stone walls accessed through the room you needed the translated code to get into. Avery will comment on feeling something weird when he walks past the ideal area for the spell -  between two torches.
• Place sulphur in the space between the two torches, this will trap zhogtk in the area but it will begin to grow and if it escapes you will die. 
• Use the incense burner, smallage incense, coal and lighter in the same place.
• Light one torch (either torch, but only one) and stand between this torch and zhogtk so that your shadow would be cast onto the Zhogtk. Make sure you do not have a light source active (ie your lighter or possibly flashlight).
• Use the Pnom book and read the spell and the Zhogtk should be banished. If any step is wrong Avery should comment on what step is missing.