What it does is far more spectacular: It reduces the HP of all enemies to 1. Its description states that it's fire-elemental, has a range of two panels, and reduces the effectiveness of equipped weapons (same as the Melt spell), and indeed, this is what it's supposed to do.

Reaper: This is the personal skill of Dark Knight Balzepho, who likewise never appears in battle.

Like all the other personal skills used by the Dark Knights, RiotBurn is a light-elemental attack that has a range of two panels, and it also instantly kills undead.

RiotBurn: This is Dark Knight Volac's special skill, but as he never appears in battle, it goes unused.

There are several unused skills in the game, as well, that can be obtained through hacking. Clearly unfinished, he's rather glitchy in battle, and even his menu sprite is incorrect. He's a Beast Tamer, and has a face portrait not used anywhere else in the game.

Mysterious Old Man: This is Gilbert/Gilbard, seen only in the Perfect ending.

Functionally, her Dark Priest class is identical to the Princess class she gets when she actually joins, but looks different.

Dark Priest Kachua: Seen only in a single battle midway through chapter 4, as an enemy, this alternate variation of Kachua works perfectly and displays properly on the menu.

(This is actually a common theme all enemy-only classes with magic capabilities can equip and use every spell in the game, although most don't abuse this benefit.) They have three spell slots, and although not that great as mages, they can use anything. However unlike the Saturn version, the player can not obtain a templar knight via using the Ogre Blade to have a player unit switch bodies with one. Not only do these guys work completely fine if hacked into your team, but their palettes even auto-adjust correctly.

Templar Knights: The all-purpose Dark Knight generic class, seen through much of chapters 3 and 4.

This makes perfect sense: why bother with extra coding if something is never supposed to be seen in-game? However, there are a few notable exceptions to this rule:

Most of these characters, while working perfectly fine in battle (albeit some non-combatants have missing animations for obvious reasons), don't show up properly on the menu, using the default sprite (a Soldier) instead.

Via hacking, it's possible to put nearly any character in the team, including enemies and even a few characters who don't even fight.

Tactics ogre characters