Guardian of Darkness
The 3 most important spells are "Drain", "Heal", and
"Blast Positive". You should always tune in these spells
to the highest level possible in each chapter. You will
learn "Drain" after mission 2. This spell will drain the
energy to recharge your energy level.
The other powerful spell that you will master later on
after chapter 6 is "Repell Energy". This spell could
reflect all of the attacking spells from the enemies and
make you immune from those spells.
You will learn a spell called "Called Spirit" on mission 4.
This will invoke a friendly spirit (a powerful one) to help
you fighting the entity. But after he destroy the entity,
it will attack you until its time is up.
Find rooms that have the most energy level. Use "Drain"
spell to recharge your energy level.
Don't start attacking the entity until it's necessary.