why the "X" is missisng?

I have the B in my notes somewhere, but not a screenshot of the symbol. Interesting that this attack is in Basque (meaning death in English), the keys and puppet show are in Latin.

For anybody wondering: Opacare = to make opaque (written over the stage in the puppet shows)
and the keys are flos, falsa, ruber, and caelum -- flower, to falsify, red, and heaven

As a little sidenote: if you work out the text and figure out the cipher before unlocking the automatic translation in game, it does not change anything. The NPC insists you don't understand him even if you give all the right answers repeatedly.