Anti-Climax Boss: Darksol. Despite being the Big Bad behind reviving Dark Dragon and the boss of the penultimate battle of the game, his physical attack is incredibly weak, and his only special only does minor damage. To compensate, he's got stupidly high hit points and getting to him requires either taking care of torch eyes up the centre where your party can be easily boxed in or going around the long way.
The Ghoul from Chapter 2, who follows up the game's Wake-Up Call Boss, the Marionette. By comparison, it's simply a stronger, faster zombie that lacks the magic or healing capabilities of the Marionette.
Balbazak is essentially a stronger variation of the previous boss, Elliot, but actually comes across as easier due to his underwhelming army and inability to move (as he's keeping the Force from entering the ship). The boss after Balbazak, Kane, has twice the attack.
Character Tiers: To list the examples would take ages. Teel;deer version: There's a buttload of differences per each game. Even worse is when there's Tiers within the own classes. (This is due to Loads and Loads of Characters, of course.)
Cliché Storm: A whole stew of heroic fantasy tropes. Slightly averted, as it helped pioneer several of them in gaming.
Zylo. Even before you promote him, his attack is powerful. After promoting him, he will tear through entire armies of enemies.
The Sword Of Light and the Chaos Breaker. Not only are they ridiculously powerful swords, but using them can cast spells as well, giving Max an effective ranged attack. Unlike other items that cast spells, they cannot break as they're plot relevant, basically turning Max into a Magic Knight with infinite MP. The Sword Of Darkness subverts this by being cursed and its effect being a Useless Useful Spell.
The Game Boy Advance remake gives you access to Narsha. Her status buffs avert the Useless Useful Spell trope fully - one very useful one is one that buffs movement.
The above is even more game-breaking if the player is using Mawlock, along with a couple of Knight cards. Buffing him up and then using the cards to attack the map's boss from across the map will win most battles after you get him, provided the force can survive whatever vanguard the enemy has set up.
Musashi. He has very high attack and HP stats. To compensate, he's slow as shit, but this can be compensated for by giving him the speed ring and feeding him a turbo pepper.
The Evil Ring. It casts Bolt 3, a power that's otherwise only available to Alef after some grinding. Its uses are limited by its chance of breaking, but that often is more reliable than Alef, especially if given to a knight or any other character with good mobility. Just don't equip it.
Goddamned Bats: Bat creatures, almost exclusively appearing in the earlier stages of the games, can avoid all obstacles and barriers, and have a good chance of putting a character to sleep with any attack. There is no way to cure Sleep, aside from waiting several rounds for it to randomly wear off.
Marionette in particular, who is also an Early-Bird Boss - she has infinite MP and can cast Freeze Lv. 3 in a huge radius (which is basically an One-Hit Kill for one to five of your units on this point of the game), and her health is always regenerating, all of which makes her insanely hard to defeat even for a skilled Tactical-RPG player.
Kane, by virtue of having very high HP coupled with high defence and is armed with the Sword Of Darkness which can One-Hit Kill party members easily.
Mishaela, for essentially being a beefed-up Marionette. Her Bolt spell is more powerful and targets a large enough area that she could theoretically perform a Total Party Killby herself, which coupled with a ludicrously high evasion rate and regenerating health, makes her damn near impossible to kill. For insult to injury, she's also a "Get Back Here!" Boss, so she spends most of the battle running away from the force, only to turn around and obliterate them while everyone whiffs their attacks. The only hard counter for this is the Despell spell, which fails 90% of the time and only a few members of the force can cast (and who will get annihilated should they fail). If it works, though, she goes from this to just a tediously long but easy boss fight, since she will never bother with a melee attack, even when her only other option is disabled.