Change is the most powerful spell in the game so level it up as soon as you can to level 5 or higher. Once done, begin to cast it on weak enemies like Goblins. A Goblin has 6 HP and 0 MP, thus switching stats with one will cause HP, VIT, SOUL, MP, and M. PWR increases.
There are two Blood Swords in the game, and they have 0 attack power and are useless for the majority of the game. However, the Blood Swords do incredible amounts of damage to the final boss and can even one-shot it.