To be able to reach the final stage you have play in Transcended Universe (level 1 is fine, no need to make things more difficult than they need to be) and unlock and equip Unknown Stone (costs 20 artifacts).
I recommend using the defensive build as the final boss doesn't remove your armor every turn.
This build centers on Defend, Faith and Punishment.
Some key cards are Blade Shield, Weekend Prayer, and Punishment. Keys skills are the ones that give you additional Faith and Punishment.
Having the Wings equipped is very beneficial, as you will be able to choose one of the four God's Choice cards, allowing you to adapt to any situation. Personally, I tend to prioritize defense in the beginning, then add some Punishment. If you're low on HP, God's Choice can let you recover 10 HP at the cost of 1 Mana, which is also nice.
This is a slow, but steady build able to sustain a lot of damage and deplete the enemies' HP with Punishment.