Whatever Tales are being told, odds are they include some awesome bosses.
Tales of Phantasia had the battle over Midgard. For players who had bought a Mecha-Halberd well ahead of time, being demoted to the Gungnir was a bit of a letdown, but flying into the sky riding Pegasus surely wasn't. The whole thing culminates in fighting a hell of a dragon boss in midair. Seeing as how the game was right in the middle of shifting into high gear here, this fight was nothing short of sweet.
The optional arena fights. Cress enters alone, fighting through a variety of mooks seen over the course of the game, when he's offered a special bonus for just one more fight. If you accept, Cress is healed, he demands, "Start the music!", "Fighting of the Spirit" starts up, and you fight the Wyvern boss one-on-one. It's basically a Palette Swap of the dragon boss described above, but it's Nintendo Hard in the best way possible. The fight tests your fighting prowess to its absolute limit, especially since you can't bring your own items into the arena. It's just a sweet-ass fight between man and dragon, set to amazing music.
Tales of Destiny has the iconic fight with former party member Leon Magnus. The fight and what follows are a dramatic peak of the game that sets the tone for the entire second half and its a tough fight with awesome music. In the Remake's "Leon Side" the encounter has even more buildup and is redone so you have the chance to play the other side, fighting Stahn, Rutee, Philia and Garr as Leon.
Most humanoid bosses in Destiny:Remake qualify since they are so tough. One that particularly stands out is the new fight between Stahn and Dymlos.
Sekundes in Tales of Eternia. Sekundes is the Big Bad of Tales of Phantasia and the series' original Well-Intentioned Extremist Dhaos. He has all of his trademark attacks and the battle has a remixed version of his original theme, Decision. Once Sekundes is below 50%, if you manage to hold him off long enough, Keele or Meredy will recite the incantation for Indignation and hit for 100,000 damage.
The cameo battle in the arena against Cress and Arche. Some gamers keep a save file just to have the freedom to fight them any time.
The battle against Rassius. Depending on your skill, the difficulty setting, and your levels, he's either really easy, or a guy who will break you mid-combo and counter with his own that include two unique attacks, and thus will beat the crap out of you, alot. Either way, the guy is so cool that fighting him is awesome in itself.
Fighting Yggdrasill for the third time at the end of the descent into the Tower of Salvation, when you can- and have to- win. It's quite satisfying to finally be able to fight equally with him and actually be potentially able to withstand his attacks instead of getting one-shotted. The final battle with him in his child form Mithos is not necessarily disappointing, but doesn't have the same impact, although you are essentially beating up the legendary hero who took on all the Summon Spirits by himself.
The third Sword Dancer. He's got tons of HP, with strong physical and magic attacks (not to mention a crapload of TP). Ya best be of high level, especially if you're playing alone; having other people tends to make battles a lot easier, not to mention way more fun.
Much earlier on there's the battle against Kvar, whose actions resulted in the death of Lloyd's mother and Kratos' wife and whose defeat is made even more satisfying by Lloyd's line at the end of the battle and the cutscene that follows.
Anytime in the series where you can go to an arena for a pleasant Bonus Boss experience, but the one that comes to mind is Tales of the World: Narikiri Dungeon 3. The arena there is all five Tales heroes in the game (Cress, Stahn, Rid, Kyle, and Lloyd) in sequence, one-on-two versus your matched pair of Original Generation kids. All of them have their full spread of attacks, outrageous HP, unmatched tenacity, and their signature Hi-Ougis. But the true win comes if you fight your way through all five of them - and meet up with Stahn's sister Lilith, who will proceed to kick your ass by channeling lightning through a frying pan. And if you beat her? You get the ability to dress your heroine up as her and gain all her attacks. Thunder Sword!
This was a real treat for the hardcore Tales fans, considering she was Dummied Out of the original Tales of Destiny and the remake had not been announced yet.
Without a doubt, the most iconic would be Luke and Asch's final duel, with the brilliant "Meaning of Birth" as BGM. Not only it's an exciting duel to play, but also it has an amazingly cathartic scenario, since Luke and Asch finally settle down the score and give closure to their respective arcs. Both characters finally stop defining themselves based on the other one, Luke completely overcomes his Cloning Blues and Asch acknowledges once again his identity as the original Luke fon Fabre. The final battle, although it does provide a Moment Of Awesome in its own right, actually pales in comparison to the emotional impact of this duel. One of the most unforgettable Boss fights ever seen in an Eastern RPG during the 128-bit era, if not ever.
Nebilim in Abyss. She has the best Strike and Fonic artes in the game. She has absurdly high stats. She also sports a plethora of Mystic Artes like Big Bang, Mystic Cage, Rending Saber, and Innocent Shine. She also brings a brand new Mystic Arte that will horrendously slaughter anyone caught in it. Prepare to die over and over and very painfully each time, especially when Nebilim uses Indignation or Fragmented End.
Cameo team battle in Abyss. You fight Reid, Mint, Philia, and Nanaly. The battle is basically a mirror fight; Reid is the sword-user, Mint is the healer, Philia is the black mage, and Nanaly is a hybrid of melee/caster. The cameo team can and will revive their teammates and use their own Mystic Artes, including Reid's trademark Limit Break, Aurora Wall, which will revive all dead party members and kill anyone caught in it. Aurora Wall is complete with its very own Theme Music Power-Up with a remix of Eternal Mind from Tales of Eternia.
Reid: We will not LOSE!
The Final Boss is an epic, three-stage (four if you count the last part with Tear singing the Grand Fonic Hymn) clash against one of, if not the, best-written antagonists in the whole series. The music is some of the best in the franchise, Michael McConnohie's voice work is just tremendouslyglorious and the fact that every character gets their own special take on the scene if they're the party leader is just the icing on the cake. It's a wonderful way to end the game and, in hindsight, it's a beautiful sendoff to the morally grey antagonists that the series became loved for during the PS2 generation.
The Duel Boss battle against Flynn in Tales of Vesperia. Some feel it loses a whole lot of impact due to the whole Fighting Your Friend aspect, rather than the ultimate clash of Flynn's and Yuri's ideals it could have been if they were fighting as enemies. Others find the duel against Flynn to be awesome for precisely that reason. It is the ultimate clash of their ideals, it's just that they're such good friends anyway that that's how they work things out - by beating each other up. Indeed, part of what makes the fight awesome is how they're so casually having a conversationwhile they're beating each other up.
Yuri: You keep getting better!
Flynn: You do too!
Yuri: Guess life's taught us both a few things.
Flynn: How many years has it been since we fought like this?
Yuri: Uh... we fought in the coliseum. You forget already?
Flynn: Of course not! Just, y'know...a lot of stuff has happened. It's-
Flynn: It's just different.
Yuri: Yeah...It feels different for me too.
Flynn: I wonder what it is.
Yuri: Does it matter? I am so gonna kick your ass!
And if that fight really wasn't good enough, maybe one of the game's many Bonus Bosses are. Specifically, the cameo battle. Tales fans must have been wondering when a character from the Gamecube / PS2 generation (i.e., Symphonia, Legendia, Abyss) would show up as an extra boss in the main series. Such a character was finally chosen for the boss fight at the end of the optional Labyrinth of Memories. That character? Kratosmotherfriggin'Aurion, the only character to ever beat out Leon Magnus in Tales popularity polls (besides Yuri himself, ironically), voiced by Cam Clarke as the original was, using all the same powerful techniques, including the first appearance of his Mystic Arte, Shining Bind, on Western shores. Clashing swords with him is just as awesome as it was back in Symphonia. If not moreso.
Team battle mode in the coliseum of the PS3 version. Your chosen party of four will fight Schwann and his brigade (Leblanc, Adecor, and Boccos), then Clint, Tison, and Nan plus a helmeted Karol, thenall four previous Tales cameos - Barbatos, Shizel, Dhaos, and Kratos...and THEN, just when you think the awesomeness has already overloaded, the rest of your party comes in to fight the four you chose. Each of these battles is like a full-blown fight against a rival adventuring party, especially the last one, for obvious reasons, and the fact that it's all in a row makes you wonder if even the PS3 is powerful enough to contain such epicness!
The fight with Estelle. Most of the second act has been building up to the The fight with Alexei and when you finally get there, he's not only got Estelle there to torment you, he forces you to fight her! And after he gets what he's after, he leaves everybody except Yuri immobile, and then forces Estelle to try to kill them again, thus leaving you in a one-on-one battle against her, to The Moonand The Shining Star. All signs point to Epic.
And also, the two fights after that if you got the true ending.
The Fighting Your Friend duels in Tales of Graces aren't all that dramatic, but they're very satisfying. The battle system is a lot of fun, but with four people on your team and multiple enemies it sometimes feels like just a lot of colour and noise. With just Asbel facing down Hubert, Sophie or Malik, though, it turns into a real test of skill. Beating Hubert by the well in Strahta is especially satisfying after his unwinnable boss fight earlier in the game. Oh, and special mention to Cheria's duel against Pascal for the same reasons, although slightly cheapened by the fact that she's just doing it to get Pascal to take a bath.