This is the editor the forums provides; there is no option to disable WYSIWYG. You can still type bbcode into the editor and it should be parsed.   I came across this (removed) thread that indicates that killing WYSIWYG mode isn't easily possible within the software: https://webcache.googleusercontent.com/search?q=cache:F2bxUNWUNnIJ:https://invisionpower.com/42TEST/forums/topic/424757-suggestion-allow-for-a-basic-editor-instead-of-ckeditor/+&cd=9&hl=en&ct=clnk&gl=u