Took me a while to figure out what team to use, and to use it right. I'm sure a super-offensive team with a really good combo maker could work, but with my luck I always failed at stage 6. So I went with a defensive team:
Leader: Holy Angel Amy (50% reduction against holy needed for stage 6 and boss stage)
Ally: Thunder Queen++ (an overpowered card, now ultimate evolved to be even more overpowered)
Erinyes++ (the other overpowered card fully max'd out level and skill wise)
Tainos (filler thunder damage with decent stats and usable skill on any stage needed)
Jotunn++ (heart changer needed when hearts eventually get low; Amy has this purpose too)
Night Witch Catherine (needed for stage 6 and boss stage)
Once Erinyes and Thunder Queen's skills are available getting to stage 6 isn't too bad. Lots of enemies have 1000-2000 defense, and this team isn't that offensive oritented.
Stage 6's Kid Saintess has 7000 defense, hits for about 14000, and has around 700000 HP. Constant spamming of medusa eyes and iron wall from here on out. The Charybdis have about 3 million HP, hit for about 17000 each, but only have 500 defense or so each. It's mostly just skill spamming with the exception of Amy and Jotunn when you get a bad break and hearts are in short supply.
The final quest is available now...I'll just post the pic of the final set of enemies you can face. If I do clear this quest I'll move it to the post I will make when it happens.
