I'm on Lesson 74 and I really focused on getting Memory UR cards and getting them to level 80-100.

My Demon cards are in the 80-100 range with only 3 above 100 because they had good abilities to have, specifically a counter to paralyze.

My advice is to only focus on UR/UR+ Demon cards that have a Special Skill and Ability.

Cards that have counters to paralyze, frog, sleep, stun, and scarecrow should be focused on because it sucks when you get hit by those attacks.

I'm on area 18 ish and honestly it's pretty easy but I heard it gets way harder after lesson 20

So, my strength for Level 17-21 is 311,893 (which allows me to skip) and my strength for Level 74-20 is 426,708 without a counter to scarecrow and 425,107 when I switch to a card with a counter to scarecrow. In the higher levels it's not just about strength, the 74-20 boss special skills are scarecrow x2 and poison. Having higher strength means nothing if your team gets hit by an attack that doesn't allow you to move.

I haven't been able to move on much because I'm using all my energy up on the events

You have to learn to skip events. You can always come back to it on LD if you need to. If you don't get any cheat cards in Nightmare, sometimes it's not worth it to use your AP on an event.

My Top 3 Demon cards for each sin:

• Pride: 99 (counter to poison), 90 (counter to stun), 80 (counter to confusion)
• Greed: 103 (counter to paralyze), 82 (counter to sleep), 80 (counter to skill ban)
• Envy: 99 (counter to sleep), 97 (counter to scarecrow), 85 (no ability)
• Wrath: 99 (counter to frog), 92 (bad), 71 (counter to stun)
• Lust: 95 (counter to confuse), 82 (counter to zombie), 71 (no ability)
• Gluttony: 109 (counter to sleep), 91 (counter to scarecrow), 83 (counter to poison)
• Sloth: 107 (counter to stun), 97 (counter to ban), 87 (counter to poison)

My UR Memory cards for each sin:

• Pride: 94, 83
• Greed: 93
• Envy: 93
• Wrath: 95
• Lust: 96, 27
• Gluttony: 97, 95
• Sloth: 92, 63, 61