What do I say to the priest to make him cooperate

Hint 1 of 7:

Actually, once you ask him for his help . . .

Hint 2 of 7:

. . . and tell him about Cerberus . . .

Hint 3 of 7:

. . . and ask him to draw you a pentacle in blood . . .

Hint 4 of 7:

. . . geez, he'll be glad to do what he can

Hint 5 of 7:

Did you give the priest the gold chalice from the Black Chapel?

Hint 6 of 7:

Before talking to the priest, did you ask the Indian how you could help?

Hint 7 of 7:

Did you read THE STUDY OF DEMONOLOGY in the house library's Humor section?