Well Call of Cthulhu has an extremely different selection of spells. Damage magic is rare. Also, sorcery is rarely used in a combat situation. That said, a pretty fearsome spell to appall others would be one of the several Contact spells. These reach out to a specified entity, who then shows up sometime in the near future, though an exact time and place might vary. So you could cast Contact Deep One, and the following night a fish-man emerges from the swamp and invades your house.