I'm looking for a book from my youth I wish to share.
One of the main characters is forced by a snotty prince to use black magic. Black magic in this world is banned from use. The mage(wizard) cries(sulks) and is a sorry lot of a lad. Using black magic makes his body fall apart. On his skin he gets boils he has to hide(or people many think he is a black mage). He knows he will die early from its use. But its death if the general public find out he is practitioner of the dark arts. Also the Prince blackmails him at this point so he can't stop. I believe the Prince is using him to take the throne from his Father, brother? I forget from who.
There is a Coliseum of the gods each part of of coliseum is dedicated to a different God. But the Dark lord (god/goddess) is banned so doesn't have a place to worship that god.
But the mage needs to do a ritual of some sort at the altar. He ends up finding a black spot on the floor and thats the place he needed. ( I believe the moon(s?) was involved. or under the star constellation that exemplifies the dark god? )
I also have am image of my mind that the book cover had a castle on it. I reminder thinking that the cover looked retarded(in my 11-12 year old mind) but my mother said it was getting good reviews.(I could be wrong on this information within this paragraph).
Around this time frame I read The Death Gate Cycle books.