Game-Breaker: Buying the staff from Lezerem's shop means free, unlimited healing outside of battle for the entire game and saves on needing to recruit a healer as the second party member.
It's Easy, So It Sucks!: Aside from a few specific cases later on in the game, nothing is really challenging if you use the demon circles in new areas to refresh your party's gear, even on the hardest difficulty.
Nightmare Fuel: Several of the monster designs if you look at them closely. Especially the Giant Toads and Midgard Heart enemies that show limbs and bodies protruding from them!
Tearjerker: Lancelorna's death. It doesn't help that it comes right after an evening of camaraderie. Just to rub it in, she even promises to "watch over you from afar" in a conversation just before everything goes south.
That One Boss: Ether Mirage will, in no particular order, remove party debuffs, power up her attack and defence, ruin your party formation, lock out demon summons (granted that that one is easy to avoid) and wreck shop with a multi-hit super. The only thing that is a constant is healing a crap-ton of health every 3 turns. Did Atlus have a hand in this horror?
- The theme when fighting against the main demon in an area and definitely says it will not be an easy battle.