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.
Demonic Spiders: Anything that can Incapacitate (prevents all actions and can only be removed with high-level status-healing items or Misha's Arcadic Cinna). Special mention goes to the eastern section of Pragma Area 2, where nearly everything can Incapacitate.
Lujits sit between this, Boss in Mook Clothing, and Beef Gate. As if being hellaciously strong and insanely fast wasn't bad enough, they can appear anywhere before you defeat Augustine in 5-1. You know someone high-up hates you when a Lujit attacks you after you meet Ayatane.
Goddamned Bats: Anything with Parry (Dodges all non-EX physical damage when HP drops below 25%), Magic Barrier (Dodges all non-EX magical damage when HP drops below 25%), or anything that can cast Evil Omen and shows up in large groups. The first two are more irksome when you're finding out that enemy has this ability for the first time in the middle of your attack.
Hilarious in Hindsight: There is an unlockable gallery image depicting the results of Demitri's Midnight Bliss on the rest of the cast. Prinny becomes a normal looking brown haired girl with a large Prinny themed hat. A little over two years later Disgaea 4: A Promise Unforgotten brought us Fuka, a brown haired girl with a large Prinny themed hat.
For some weird reason, Lyner and Ayatane are like this even though Lyner has three chicks with him.
For some reason, York is not as much of an ass to Lazarus, even insisting on letting him get away, when he was a member of the enemy Twelve Knights... It's possible that's because he's a fellow gunslinger, and many of his values echo or identify with his own (perversion aside). Their distinct similarities is the reason that their last match is a duel, and why York spared him.
Morrigan, beingMorrigan, has this since she flirts with most of the cast. Special mention to her calling Felecia "kitten."
Scrappy Mechanic: Having to pay your own party members for supplies, healing and other services in Cross Edge, and prices tend to be fairly expensive. Great, so if we all get brutally killed in a battle due to lack of recovery items or decent weapons and armour, we'll all know whose fault that was.