Banished from Heaven Trophy in Nun Attack

Story Related, cannot be missed
The final boss and easily most brutal of the boss fights. Take as many Resurrection miracles as you can  (I needed 8 for this fight, I came in with 15) and 5-10 Shield of Faith miracles. Save as many as you can for Mortanna herself.

On the way to the final boss, there is 3 sub-battles. In each, you will have to fight one of the previous bosses again. This time a slightly stronger version of the previous. The third sub-boss, Viktor, will use his confusion spell frequently, making this battle much more dangerous than the last time you fought him. If you have trouble with him, then equip Purity as your third miracle. If not, take Restoration to make the final fight easier. You can do it without it, so the choice is yours.

Once you reach Mortanna, she will attack you relentlessly with a barrage of physical attacks and energy bolts she shoots out. Occasionally she will grow a tail that whips out and hits your characters as well. When she disappears off the screen, a rain of fireballs will come down and do a lot of damage. When this happens is when you want to use your Shield of Faith miracle to dampen the damage taken.

Keep your characters spread out so they all don't take damage at once and don’t waste any time with offensive miracles. You will need to spend all your time healing and resurrecting your characters. A lot. After each round of fire rain, Mortanna's health will restore a decent amount but if you keep all your characters alive it will only take 1-2 minutes to kill her. Other than that, just keep firing at her when she is on screen and make full use of all your characters special powers.