Confusion
Tut, if you actually have some demon ichor, it would probably work fine. Roll Alchemy if you want to make some mirror oil with the reagents on hand... of course, you'll have to specify what you're using.
It's unlikely that the mallet is somehow directly involved. Your fellow PCs could tell you that the last time they were here, they had some mirror oil and applied it directly to the mirror, causing it to open into a portal.
...
Marivhon, you cannot understand any of Renwick's spellbook.