Background: Not much is known about the Sorcerer. He is leading a city of Dark Elves who want to take over Allansia and he has kidnapped a Storm Giant with the idea of learning what he knows.
Prominence: From paragraph 1, you learn that the Sorcerer's shapeshifting (and sometimes bat winged) dark elves have infiltrated all communities in Northern Allansia in order to drive them apart and cause strife and warfare. He is smart enough to send servants to a tomb in order to retrieve a magical amulet that will cause his downfall. He also cuts of Sardath with a magical storm. 8/10
Hardness: You never get to know the sorcerer's stats because if you try to fight him, he utters a spell preventing your attack and then drains your life. Unlike most gamebook villains, the sorcerer does not underestimate you and converses with you to discern your weaknesses. You can only defeat him if you have the amulet, have the right number on the back and say the correct things. However, once you know the correct conversation, you will always win. 7/10
Ambition: Taking over Allansia for the Dark Elves. 9/10.
Style: The Sorcerer has a very imposing figure despite his profession. His Dark Elf lair also has some insanity inducing architechture. Also instead of the standard villain lines, you can also have quite a pleasant conversation with the sorcerer. It's almost like he's a bond villain, who are always very stylish. 8/10.
Diabolical genius: He has created bat winged dark elves and a shapeshifting potion. He is also trying to break the will of a storm giant. In fact, simple combat is the last thing this guy would take part in. 8/10.
Total score: The Sorcerer is a sophisticated villain who has covered all of his bases and requires a lot of effort to take down. 40/50.