There's only 3 to learn, but in order to learn any of them, you first need to talk to the people in the Succubus Tower library (no, you can't skip this part), and then tell Rinny you know to beware The Watchers.
1st spell is free.
2nd spell requires Mystic stat to be 7+
3rd spell requires finishing the Manor quests first, and to have seen Rinny grow a penis at least once.
Bell also needs you to have visited the tower and finished the manor.