Accidental Aesop: The original Japanese script involved a smuggling ring of illegal opium in Edo. The 1991 official English localization could not mention such drugs, so changed opium to "bananas". An NPC lampshades this by asking why bananas have to be illegal in the first place. It's obvious to most players that criminalizing bananas is silly, and the sheer organized crime involved might not exist without a legal ban on bananas. In the real world, this is an increasingly vocal argument against the War on Drugs, especially after a 2011 United Nations commission declared the international War on Drugs to be a costly, violent failure — drug crime and drug violence are usually caused by drug bans, not vice versa.
Awesome Music: You will be tapping some beats if you play the game with the sound on.
Save The World, the music that plays during the Final Boss battle in the third and final phase, as the Arsenal starts using the Smasher attack. It's also quite intensive and badass-sounding. Even more so awesome is the DS remake's version of this theme.
Complacent Gaming Syndrome: It's not uncommon on most runs with a monster to keep them as a Fairy (which have a lot of useful spells, especially if you get them early enough) or Ghost (which have a lot of useful skills that bypass a lot of resistances). Both are good healers and in the case of the Fairy, Titania is considered by most to be the best monster in the entire game. They're locked at the Central Shrine though, being only accessible after eating the meat of one of two of the mini-bosses going down the escalator.
The Cocatris enemies found in the Nasty Dungeon, Final World and Final Dungeon. They have a habit of petrifying your party, counting as an instant kill and requiring you to use Soft to cure them. Forgot to bring Soft? You're one party member short to deal with the War Mech. It doesn't help that in the Final Dungeon they're generally accompanied by Sylphs who love to spam the Tornado spell that hits your entire party. And keep in mind they come in packs.
Game-Breaker: The Excalibur. It deals a minimum of 1,050 damage (before defense and weapon resistances, of course), hits a whole group, never misses, and unlike other weapons, never breaks.
Inns only charge money to recover HP. There's nothing preventing you from using your Mutant's or Monster's healing spells and then sleeping at an inn for free to refresh the spell charges and using the money for invaluable gear.
The random encounters, when used to grind items and stats, are exploitable. Saving the game and restarting the system reset the RNG - so if the first encounter on turning on the system was a battle that gave you a stat bonus (or item drop), saving and then restarting the system was GUARANTEED to trigger the same battle with the same reward. Finding a battle with a HP, Strength, or Agility increase and exploiting it in the first couple worlds would give you a character with 999 HP, 99 Strength, 99 Agility, creating both a Disc-One Nuke and Game-Breaker.
Good Bad Bugs: A certain enemy, when inflicted with the confuse status, will attack itself with Punch for upwards of 6,000 damage (Punch does more damage the fewer uses of it are left, and the enemy is using a Punch it doesn't actually have).
An infamous bug involves you teleporting off the Dragon Racetrack while on the dragon. This completely breaks the game as you can walk through walls, allowing you to visit ultra high end dungeons early, steal helper NPCs from the end of the game, etc etc.
There is a way to give your robots infinite agility. Equipping a martial-arts ability on a robot boosts their agility. Completely use up a martial arts ability that's equipped on a robot, and even though the item is gone, the game won't recalculate the robot's agility and they'll keep the boost.
The game is not good at handling enemies dying due to poison. Many speedruns exploit this to varying degrees.
Heartwarming Moments: Quite a few for such an early RPG. But one that stands out is the hero and their whole family going on an adventure together at the end of the game.
The game has a "Mr. S", the Cool Teacher that helps your party. Come 2003, a film has another "cool teacher" (or at least becomes one) that calls himself "Mr. S"...
The Indiana Jones expy is your father, who all but abandons you to your mother while he goes out on adventures securing relics to save the world. Come Indiana Jones and the Kingdom of the Crystal Skull, seventeen years later, it's almost exactly what Indy did to his son Mutt Williams in the backstory.
Nightmare Fuel: Apollo's demise. How about the "silently screaming" faces in the walls of the not-quite Final Dungeon?
The arrangement of the dungeon theme used in the remake. It begins with shrill, descending notes and breaks into a throbbing baseline that sounds like nothing so much as something big and scary coming to eat your face.
Self-Imposed Challenge: Using intentionally unbalanced parties (such as four robots or four monsters) is a popular form of self-imposed challenge with this game.
The final boss' Smasher ignores defense and distributes damage randomly among your party.
Apollo's Flare, dealing almost 1,000 damage to everyone it hits (instant death to one if you didn't raise its Spirit (Mana) high enough). Especially in the remake.
Much earlier in the game, Ashura's Six-Arms attack. It's very possible for your Guest Star Party Member to be the only one capable of doing appreciable damage to the boss, and if you didn't think to outfit a Robot with multiple layers of armor, you'll be watching helplessly as Six-Arms chews through your entire party one insta-kill at a time and praying that your Guest can kill the boss before then.
That One Boss: Venus and Apollo tend to be stumbling blocks for many players. Though Apollo will die on his own, so you can just sit back and heal constantly.
Odin as well. The OdinCrows with him can throw unpreventable damage on your entire party. Odin himself has Gungnir that can one-shot anyone in your party (unless they have 999+ HP and good armor — or O-Weapon). (Hint: equip one of your members with the Aegis magi and use it each round).
It's actually advisable for the whole party to die at least once during gameplay, because if you haven't died at all up until you reached Odin, then the fight with him will be much harder.
That One Level: The Nasty Dungeon, self-consciously so. Technically doubles as a Bonus Dungeonand a Breather Level, since that world's only MAGI is found right by the entrance.
The remake provides examples of:
That One Attack: The Defense System's Double Starburst attack, which tends to hit for about 550 HP of damage and which it will use on every turn past a certain point. If your healer isn't the first to attack by the time it begins using this move, you're dead.
is a quite catchy and iconic even for Game Boy soundfont standards. And then there's the remake version of said theme