The Alter of the Chaos Mouth doesn't seem to be working. What am I doing wrong?

[GL - MB]

Just to say it happened, I took all the items to the altar and put them in. The tear, the mask, the Scourgestone, the Diadem, the star (comment edit, thanks to Dead God's comment), and the trepahedron (don't care if it's mispelled). Once the items are in, they are supposed to transmute into the keystone.That didn't happen. Nothing happened. Did I miss something?

[Eldritch God]

Maybe the star of the champion , drops by the undead dragon in the arena.

[GL - MB]

Yes. I had that in there. Sorry about leaving it out of my post. Was typing off the top of my head. I watched a video on youtube that showed all the items being put in the altar. I repeated that. Didn't work. Maybe a bug? I will edit my post to correct the omission.

[OGImmortal]

You have to add the Scourgestone as well. It took me a while to figure it out.