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.
Creepy Child (Depending on who you ask, the anime might extend to this, too)
Nightmare Fuel (The Persoenlichkeit's strongest attack involves her familiars pinning down its target. Alfimi gets up close and personal, unsheathes the Lichkeit's katana and stabs the living shit out of it. Skewering motions make the sight of the attack painful, until you realize Time Stands Still during the attack, meaning the target isn't even feeling anything until afterwards)
OT3 (You think Kyosuke will just settle for Excellen and not both her and a loli clone? Fanworks say you're wrong)
Try OT4...of sorts: before her return in Original Generation Gaiden, there existed a LOT of fanart featuring the "Nanbu family" and their very, very cute twin daughters. See Dead Guy Junior for more
That One Level: The final stage of Cosmoquake. The player starts out having to face more than a dozen Dancougar enemies with 18000 HP and 30% HP Regen. (To put this in perspective, a well-upgraded attack might deal 3000-4000 damage without Spirit Commands.) After shooting down enough of those, a large number of Einst appear on the scene, including one Einst Regisseur. If all of that wasn't bad enough, Machine Robo enemies show up around the fifth turn. Top it all off with a huge map and a 20-turn time limit, and you have a stage that can become nigh-unwinnable without the proper preparations. Or the player could just grind by repeatedly getting Game Overs; it's not like Compact 2 has a big secret involving turn count or anything...
Galaxy Showdown gives us the mother of all indoor SRW stages with the Machine Robo finale. The player's entire team is pre-determined, and consists of the supporting cast of Machine Robo alongside Excellen, Billbine, Gundam Ez-8, ZZ Gundam, Gundam F91, Raideen, Getter Dragon, Mazinger Z, and Daitarn 3. Unless the player somehow managed to keep all of those units up to date (unlikely, given the game's very strict Arbitrary Headcount Limit), they're in for a slow, painful corridor stage. At least Rom Stol shows up mid-way through to help out.
You'd expect: For Gai to stay close to the Nadesico, as Aestivalis units guzzle energy and the battleship in question can quickly recharge it.
Instead: Being Gai, he charges headlong towards the Jovian Lizards and burns all his energy just getting there, therefore becoming unable to move and thus requiring Akito Tenkawa, in his own Aestivalis, and eventually the Gandor team to bail him out.