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: Ghost Summoners in Summon Night 3. They are immune to all status effects including possession, can teleport, and ARE NOTsquishy wizards. They are found in both plot and non-plot battles. Their prevalence is also justified by the plot.
Game Breaker: The MP restoring party skill in Summon Night 3. Once you earned that skill, the playing field changes dramatically. You no longer need to be as conservative with your casters and can win just about any battle solely via attrition. In Summon Night 4, this was moved down to be the last unlockable skill. It's less of a game breaker there due to the comparatively lowered difficulty.
Swordcraft Story 2 gave a crazy amount of buff on drill: It hit multiple time with down attack command and its rather Difficult but Awesome Charged attack, sturdy yet economic in term of weapon durability, deals massive damage, can hit above for combating airborne enemies, and Drill special, which cost really cheap deals higher damage than the supposed to be strongest special that sacrifice your weapon if it connects(and its easy to aim).
From the same game, the increase defense spell. It also gave super armor due to how the defense system works which cuts difficulty of many a boss in half.
Good Bad Bugs: In Summon Night 4, Glad will keep his Block wait stance if you de-level him via Xiao-Mei's Book of Rectification.
Les Yay: Sugar kisses Pratty and tells her she intends to marry her, female or no. And that's only their initial meeting. There's so much Les Yay in the Swordcraft Story games it's staggering. And she only kisses her if she's female.
Razzy doesn't gain a crush on you unless you play as Pratty.
Aside from from Sugar related dialog, there's plenty with Sanary. One conversation has her even flat out say she's not interested in (those) boys. Pratty claims that Sanary in a French Maid outfit is "cute".
The second game features Lynn, who is pretty much Les Yay incarnate. One of the main character's options in the second game is to spend a night with Lynn in a secluded area, where she promises to teach you about love. It fades to black after you start discussing kissing. Honestly, this is well past Les Yay and straight into Gay Option territory.
Every night you spend with Dinah as Area slowly breaks through that Tsundere exterior bit by bit, and she blushes a lot whenever Area complements or praises her. By the end of the game when Area says she will be by her side from then on as partners:
—>Dinah: I don't have a choice, do I? But if I had one, I would probably stay with you anyway.'''
Nightmare Fuel: But just a little bit. Arno's song is somewhat disturbing.
(referring to wind) It blows beneath your bed, and chills you till you're dead...
Summon Night 3: Chapter 12's second battle. It's more than just a standard double whammy double stage (after a battle that included FOUR named enemies). Here you start with two WOUNDED guest characters (cutting your own party down to six) whom start nearly surrounded, and both of them must survive in addition to the usual We Cannot Go On Without You. It doesn't help that almost all the enemies can deal some of the more crippling Standard Status Effects with their attacks, are immune to most of them, and have ludicrously high TEC granting them ridiculously high hit/evade and critical hit rates. To top it all off, the enemies here will begin to charge your party after a set number of turns have passed meaning you can't take your sweet time. If you are not planning on Level Grinding and are attempting a Brave Clear, you will NEED a certain expensive accessory for ALL six of your party members to guard against the status effects just to even have a decent chance. Less if you are using the immune to Standard Status EffectsOptional Party Member robots. Let's hope you didn't saved right after the previous battle without an earlier save...