The Roguish Thief: Gutsco

Gutsco is a thief that has been harassing the Dwarves of the Dwarven Hallow. Prior to the Warriors of Light's arrival, Gutsco stole one of the dwarves' horns of ice and fled into the nearby underground lake. The Warriors of Light defeat Gutsco and return the horn without incident...

...Or so it seems. In actuality, Gutsco had turned himself into a shadow and followed the Warriors back to the Hallows. There, he managed to get past the force fields and snagged both horns so that he could enter the Molten Cave to the north and get his true prize: The Crystal of Fire. y the time the Warriors of Light manage to find him, he has already gained more power from the crystal and seeks to beat them to fully gain the crystal's power. Then, he transforms into a Salamandar.

Gutsco is a bit of odd mood whiplash. Prior to this was the Tower of Owen, which concluded with Desch sacrificing himself to fix the tower's reactor and save the Floating Continent. Then... you fight some petty theif who wants the Fire Crystal and has no connection to Xande (whom you just learned about). His dialogue is even casual and, in the remake, goofy. Then he turns into the doofy looking Salamander and wipes your party with flamethrower.

Not helping matters is that he's right before Hein, who's something of a signature boss for this game.

Of course overthinking can make even this random guy intriguing. Most interesting about Gutsco is that he is one of few characters to directly use the Crystal's power. The final boss of FF1 does use the crystals' power, but outside of him and Gutsco, there aren't that many cases where that happens. The key factor between the two characters in question is that they both turn into tangently related monsters: The former taking cues from his armor (especially in later appearances) and the latter from the serpent around his body.

Or perhaps, this is merely overthinking it.

Upon gaining the Fire Crystal's power, Gutsco puts on a demonstration by transforming into Salamander. Despite looking like a bumbling lizard with goofy eyes, Salamander is no pushover. He hits hard for that part of the game and his Flamethrower attack hit everyone in the party and will likely kill all of them except the guy who has the ice equipment. In particular, Salamander may be the one boss that's harder in the Pixel Remaster because he now spams flamethrower almost every turn.

Interestingly, the remake recolors Salamander to be the same color as the snake around Gutsco's. The Famicom and PR versions color it blue or purple instead.