These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: The final boss is extremely disappointing, especially when compared to (say) huge complicated fights earlier on like the Eye of Valmar — he has only one part, does nothing but try to spam powerful spells at you over and over in a game where that strategy is trivial to counter, and even if that was still a threat at that point in the game he lacks Contractual Boss Immunity to Spellbinding Eye, meaning you can keep him paralyzed permanently and ensure that he never gets a single turn.
Game Breaker: The "Spellbinding Eye" technique can turn anything into an immobile, incapacitated punching bag. In a subversion of Contractual Boss Immunity, this includes the final boss.
Equip one character with maxed out Attract ability, to ensure they are the only ones ever attacked, along with every defensive skill book ability you can find, then have then defend every round. They will be taking single or low double digit damage even at the end game, rendering every boss a joke.
Early in the game (really early), you can fight enemies that drop an item which permanently increases your Defense. Grind enough and you are practically invincible.
The only way to get killed using those is when facing the Bonus Dungeon's Demonic Spider enemies that can wipe out your party in one hit. The Valmar Pieces and Pope Zera-Valmar are ridiculously easy.
The ability that reduces the action-time cost for using items is also a severe one in combination with the reusable staff that does an AOE attack... which delays the turn of anyone it hits, meaning that with someone using it at enhanced speed, most enemies will barely get to act at all.
Fridge Brilliance: Why is Ryudo able to resist being possessed by the Horns of Valmar? It's because the pieces of Valmar feed on people's desires, either good or bad, and at this point in his life, Ryudo had become so cynical and apathetic that he had no real desires, beyond his survival and that of his friends. The Horns had very little to feed on.
Nightmare Fuel: The game is full of this really, only partially covered up by the cute graphics.
The Moon of Valmar is in fact a gigantic egg, complete with an enormous eye looking down on the world below. Oh, and Mareg, the Beastman who's been a part of your party for two thirds of the game? He dies torn apart and eaten alive by hundreds of critters.
There was also the part where you enter a young girl's soul, which, due to her internal suffering and Demonic Possession, gets more dark and twisted the further in you go.
Selene releasing the Heart of Valmar. Yick.
Player Punch: Mareg's sudden, brutal, and utterly selfless death. Rather than worry poor Tio (who is beside herself), he stays behind at the bottleneck and smilingly says that he'll be right along. He's doing this with a mouthful of blood, you see.
The PC version even more so. It's possible that Millenia, during her Hopeless Boss Fight, will not end the fight to progress the story, and will just wear you down until you inevitably start over (this happens if you run the Tutorial in the Carbo Village Weapons Shop before fighting Millenia). It's also possible for the characters' mugshots to randomly replace item textures in battle, so monsters drop Millenia coins or Roan bombs.
Tear Jerker: Pretty much everything involving Aira. She was born with poor eyesight, and, when she is seemingly cured, it eventually turns out that she was actually possessed by the Eyes of Valmar. On top of this, her mother's efforts to cure her sight beforehand get her labelled as a witch after the fact, turning the entire village against the both of them. As if this wasn't bad enough, all the girl wanted was for everyone in her village to stop fighting and be happy, when, in reality, she was actually causing the the suffering they were currently going through. Add to that a Priestess intent on "purifying" both her and her mother (and the village itself, at the rate things were going) simply because she was possessed, and the poor girl finally snaps. In the end, the Eyes Of Valmar are removed from her, but, in the process, a portion of her soul is destroyed, leaving her alive but comatose. The townspeople, upon realizing what happened, are so stricken with guilt that they can barely function, and the party is more or less marked as an enemy by the aforementioned Priestess, who, despite all that happened, was still intent on "purifying" everything, though she reluctantly stepped out after urging from the villagers. She eventually recovers, but still...