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.
YMMV: Tales of Destiny
Complete Monster: Barbatos Goetia, a man so evil that, after his defeat by Dymlos, his name is removed from history altogether. After Elraine resurrected him, Barbatos happily became her Dragon in order to mark his name in history (and be praised as a hero instead, as seen in an alternate timeline) and has no qualms about murders, be it for missions or for the heck of it. The first time we see him on-screen during the flashback, he crosses the Moral Event Horizon by holding Loni hostage and forcing Stahn and Rutee to drop their weapons, and then proceeded to outright murder Stahn and cripple Rutee, all in front of young Kyle's eyes. In the present, he also tried to kill other heroes like Philia and Garr/Woodrow just to eventually get himself marked in history.
Draco in Leather Pants: A hotly-contested example in Leon: it's unanimous that he's a complete dick with sympathetic reasons for what he's doing, but fans are divided on just how many squishy points this gets him.
Ensemble Darkhorse: Leon Magnus constantly tops favourite Tales series character polls in Japan, returns in the sequel as Judas, and has a tendency to appear as a major player in other games like Namco X Capcom. The remake even gave players an option to use him as the main character. But he still dies the same way.)
Leon's ascendancy seems to have been eclipsed by Yuri-Freaking-Lowell, but considering Judas ranked as the 29th most popular character, were one to combine the number of votes Leon and Judas each gathered, Leon is still the most popular Tales character.
It's to the point now that Namco has officially retired both Yuri and Leon into the Hall of Fame for the popularity polls. They can no longer be voted for in the official main poll for most popular Tales character.
Kongman is a rather hilarious example, actually. He's a very minor optional character in the original, but his portrayal in the remake vaulted him into popularity. People love to hate him, and Namco's bonus DVD's waste no effort in ripping the piss out of him.
Lilith's quite popular, considering she's a minor character.
Game Breaker: Leon is arguably the strongest character in the ToD remake. He may have crappy defense and low HP, but once powered up, he can kill things before they even have a chance to lay a finger on him. Let's see...
Combine Chaltier with his Chaser ability that grants extra CC points, and if you get critical damage, you can kill any normal monster with a single combo. Oh, and Leon has the highest critical damage rate.
Geneijin is more spammable than spam itself.
Then there's "Marian...". Sword Artes typically hit nearby enemies or far away ones. With this one you can hit enemies that are close and far away by creating a damaging force field and firing a Sword Beam. Oh, and by the way, Leon is immune to damage while he's using it.
Arte extensions. You know how a character can normally only have 4 artes equipped at once? Yeah, about that...
Demon Lance Zero is also more spammable than spam itself. It also doubles as a self buff that gives 5 Penetrate with each use (can't be staggered for the next 5 hits).
But he dies long before we even get to the Big Bad! How do we fix this? That's where the Narikiri Dolls come in, a set of items that allow you to give any character the skills, balance, and sprite of any of their teammates. Though you can't get them until very late in the game, Leon's is the cheapest, and you can get multiples of each doll. Which means you can have a battle party of 4 Leons. Have fun.
For a change of pace, how about Johnny/Karyl's ultra-cheap Maware Rondo?