The game's ending FMV shows the Warrior of Light walking towards Cornelia Castle in a camera angle mirroring the opening of the original game.
The Warrior of Light's Fire, Ice, Lightning "Fang" magic attacks are named after items that cast elemental magic. If you look closely when he attacks with them, you can see he's actually throwing an item into the air, not casting the spell himself.
Of course, all of those are Black Magic, and the Warrior of Light is a Fighter/Knight, who had no access to it in the original.
The Warrior of Light's Victory Pose when confronting Garland and ending his EX Burst mirrors the original artwork of the Knight.
When you find the Bahamut summon in the Warrior's storyline in Dissidia 012, Bahamut says "Long has it been since men of courage have stood before me.", the same thing he said when granting you your Prestige Class in the first game.
Garland's sword has five forms, and aside from the base greatsword, each form references one of the Four Fiends and their elemental attack that Chaos is able to use in the final battle of the original game — the whip is used when casting Tsunami (Kraken), the twin swords are used for Blaze (Marilith), the Lance is used for Tornado (Tiamat), and the axe is used for Earthquake (Lich). His Flare attack in 012 retains the base greatsword form, reflecting that Flare is Non-Elemental.
Garland is fought as the first and last boss of the Warrior's story, just as in Final Fantasy (okay, he transformed into Chaos for that last battle, but still).
When taunting the Warrior of Light, Garland's line "You will meet your end here, and I will live forever!" is a paraphrase of what Chaos says before the final battle.
Firion's fighting style reflects the entire battle system and the different weapon types — swords, bows, lances, daggers, axes, staffs, shields, and barehanded. In fact, pretty much the only thing you can do in this game that you couldn't do in Firion's original game note that isn't only different because of the gameplay style is shoot your other weapons out of your bow.
His knives are charged with electricity. Leila, the character who fought with knives in the game, joined the party with the Thunder Spell.
Whenever Firion fires an arrow, the bow flips forward, the same animation for bows in the original game.
Firion's interactions with Shiva are an impossible-to-miss reference to his seduction by the Lamia Queen. The poor guy will Never Live It Down.
Firion has a trademark pose, appearing in the most well-known concept art of him — he holds his arm out, sword horizontal in front of his face. This appears twice in Dissidia — in a cutscene, from the same angle, right before he fights The Emperor, and as the very end of his match-start animation, before he sheaths the sword, though this one is harder to notice due to the angle of viewing being different than the art piece.
The Emperor's Shock and Awe spells refer to the fact that his only offense when fought in human form in the original game was a Thunder X spell.
The Emperor's ground Flare is blue, while everyone else's Flare is orange — in his original game, Flare has an animation of blue fire as opposed to the rest of the series where it's orange.
When defeated in the final storyline, the Emperor mutters "How could I lose, not once, but twice? Who are you?", which is what he says when slain in the final battle.
The Emperor's perfect EX Burst, Entice, is a reference to the Lamia Queen boss, who uses the same skill to... seduce and confuse Firion. Um...
The Emperor's death cry whenever he's defeated in battle is his signature "UBOAAAA" or "UNGAAAAAAH" depending on the language. Tidus even lampshades this:
The Onion Knight's swords take their appearance from the concept art of the Unnamed Warrior. His pose when finishing his Ninja EX Burst is, you guessed it, also from concept art.
Open up the other menus during his EX Burst — every other item, spell, and weapon you see is something from the original game.
Both his EX Bursts copy the style of battles in the original game, right down to him taking a step forward when his "turn" is up.
When using her EX Burst, and in the Onion Knight's EX Burst, the Cloud of Darkness poses in the same way as her original sprite was positioned. Particularly notable for her, since all other characters just use their "idle" poses when Onion Knight uses his EX Burst on them.
Kain's EX Burst quote, "Let me ease your pain", is what he says when preparing to kill Cecil at Fabul. Well, to be specific, it's "let me ease your suffering", but same idea.
The pose Kain has when at the end of his successful EX Burst is the same pose he is seen holding on the game's original logo.
Kain's Spiral Blow and Sky Rave attacks are Band skills from The After Years.
The Onion Knight says to Kain "can you catch birds with that jump?", serving as two references — Kain's DS minigame where players had to swat away birds as he leapt into the air, and the Garuda from III, widely considered That One Boss unless you spammed the Dragoon's Jump attack.
The Shadow Dragon's Black Fang and Binding Cold attacks are taken from the boss battle with Golbez. Twin Meteor is his Combination Attack with Fusoya.
When someone other than Cecil beats Golbez in Shade Impulse, he says "The flesh may rot, but the soul never perishes...", which is what Zemus said when Golbez and Fusoya killed him.
Golbez randomly says "Allow me to give you something" when using Gravity Force, and says "A gift!" when using Gravity System and Float System — when he met Cecil at Fabul, Golbez said "Allow me to give you something - a gift to remember our meeting by."
His Cosmic Ray is based on his cutscene attack where he knocks party members aside with lightning blasts from his hand.
Bartz's EX Burst opening is the exact same animation as the Spellblade ability — he raises his arms, his swords fly out in four directions, turn into orbs of energy, and flow back into him.
Similarly, the animation for Goblin Punch is the same too, and features the same blue diamonds and star graphics.
Bartz cries out "Sweet Cosmos, it's a talking rock!" when he finds the Leviathan summonstone, based on his line "Sweet Christmas, it's a talking turtle!" when he first met Ghido.
Bartz's combo attack from Holy to Flare refers to the Fork Tower, where the two spells lay inside twin turrets at the top of the tower.
His Mirror Match quote "how about we have a staring contest" refers to the Bonus Boss Gogo — in order to beat him and get the Mime job, you had to sit there and do nothing.
Exdeath's lines "prepare for the afterlife" and "anger and hatred cannot defeat me" are taunts he tossed at Galuf.
Exdeath's Bravery Attacks (such as Vacuum Wave and Reverse Polarity) are based off his moves from the first fight against him, while his HP attacks are based on the Neo-Exdeath battle.
His line in the final storyline, "All shall be returned to nothing, as will I... For eternity!" is a paraphase of Neo Exdeath's Badass Boast introduction.
Gilgamesh's weapon arsenal is made up of weapons he has or could have collected — the Excalibur, Excalipoor, Masamune, and Zantetsuken are his summon attacks, the Chicken Knife was in his original game and there's more to that The player can only get the Brave Blade or the Chicken Knife; the other is Lost Forever. Since apparently Bartz took the Brave Blade, that left the Chicken Knife behind and presumably Gilgamesh got ahold of it somehow, the Genji Katana of course refers to his trademark Genji equipment, and the Naginata and Battle Axe are weapons his sprites are holding.
The Genji Katana specifically takes its appearance from Auron's Genji Katana. A bit of Fridge Logic there, since we never see Gilgamesh visit Spira, but apparently he got there somewhere along the way.
His taunt when using Jump, "Fell for it!", is a joke on how he likes to pretend the party has beaten him, then casts status buffs on himself and uses a Jump attack.
The job cards of the Duel Colosseum and Labyrinth are based on the game's Job System, the latter having every job class from the game aside from the Game Boy Advance-exclusive jobs. The abilities are based off an ability the job teaches in V, and the images on the cards are based off of the appearance of the job in this game (more noticeable with jobs with inconsistent looks, like the Blue Mage and Chemist).
Terra's EX Mode bonus description reads that she "embraces the spirit of a magus" — in the original game, the Dualcast ability was attached to the Soul of Thamasa accessory.
The unique accessory Terra wears when Kefka controls her is the Puppeteer's Wheel, a mistranslation of the Slave Crown she wore in the original game.
In 012, Terra says she feels nostalgic looking at the snowfields, a reference to Narshe.
Her relationship with Vaan and Onion Knight are a collective reference to Locke.
Aside from Flood and Thundara, all of Terra's attacks are spells she or Celes could learn naturally.
All of Kefka's attacks are attacks he uses in the final battle, though his Fire, Ice, Lightning spells are given wacky twists.
Many of his one-liners from the original game made it in:
"Don't think you've won this!" and "Graaah! I'll remember this!" are from his defeat at Narshe.
When facing the Emperor, he says "You're less than worthless!", based on what he says when he kills Gestahl. His Extra-Crispy Firaga quote "You'll be well-done!" is taken from the same scene.
"You're lower than lower than dirt!" and "That hag isn't worth the dirt on the bottom of my boots!" paraphrase his taunt to the party, "You may as well be the dirt on the bottom of my boots! Or the dirt stuck to the bottom of that dirt!"
When Lightning tells him and the other Warriors of Chaos to step aside, Kefka replies "'Step aside' she says. Do we look like side steppers?". When he ran from his battles with Sabin, Sabin called out "Wait!", and Kefka's response was "'Wait' he says. Do I look like a waiter?"
When preparing to fight Vaan, he says "You're about to learn why 'oppose' rhymes with 'dispose'!", the same thing he said to encourage his troops when he attacked Narshe.
Pretty much all of his dialogue in the final storyline is taken from his pre-final battle speech in the original game.
When Kefka begins his EX Burst, three colored circles appear over him: blue at the top, yellow on the left, and red on the right. The Warring Triad, the gods he absorbed his power from, are in the same positions atop the Floating Continent — the blue-clothed Goddess was at the top, the red Demon was at the right, and the yellow-winged Fiend was at the left.
Kefka catches Kuja planning to sneak Zidane and his friends behind enemy lines and interrupts them, claiming it was Kuja's plan to lead them there and betray them all along. He pulled the exact same stunt on Celes and Locke in the Magitek Research Facility.
He pulls a similar stunt with Terra and the Onion Knight, telling them how Terra attacked the Onion Knight. The twist being that he's actually telling Terra this, as the Onion Knight already knows, and Terra lost her memory of the event.
In the end of the Onion Knight's story, Terra (who was forcibly transformed into an Esper and attacked him earlier in the story) is lying unconscious, and a concerned Onion Knight has Terra's situation explained to him by Golbez. Golbez tells him that Terra is afraid of what she is, and that she needs some time to come to terms with her situation. The whole setup is very similar to the visit to Zozo, after Terra transforms when speaking with the Frozen Esper. The leader of the playable party is approximated by the Onion Knight, and Golbez takes the place of Ramuh.
Terra's Crystal has a shape similar to a Magicite crystal.
The camera angles in Cloud's confrontation with Sephiroth mirror many of their battles in other games — see here◊ for a comparison.
All of Cloud's limit breaks appear as attacks.
The "Allure of Honey" equipment set refers to the infamous Wall Market cross-dressing scene — the Sexy Colonge, Member's Card, Blonde Wig, and Silk Dress were the best items you could find for the subquest.
The gateway that Cloud confronts Sephiroth at in 012 is at Mount Gulg, a circular mountain in a field of snowy peaks — it's the Northern Crater! ...okay, technically Mount Gulg is in the south, but the point is the same.
Two cross-company gags, Tifa has an attack called "Falcon Dive", and her Premium Heart gloves have the Kingdom Hearts logo on them.
Tifa begins her EX Burst by landing on the "back wall" and jumping off to kick her opponent, the same move she made when fighting Loz.
Sephiroth's "Oblivion" is the attack he begins his Kingdom Hearts II boss battle with. Shadow Flare's original graphics in the Japanese release of the first game took their appearance from the Kingdom Hearts series, too.
Hell's Gate is the attack he used to kill Aerith. This was taken to its logical extreme in 012, where the AI is specifically programmed to use Hell's Gate on Aerith when she's called as an Assist to use Holy.
His victory quote "Know your place" is also taken from his Kingdom Hearts II battle.
He warns the Emperor when facing him "don't fall for your own traps." This is the same warning he gave Kiros and Ward in the Centra Excavation Site, "it'd be idiotic to fall for our own trap."
Ultimecia's quote "Reality is harsh, is it not?" is a reference to her speech at Deling City while possessing Edea. The reference was Lost in Translation though, since the English speech differed greatly from the Japanese.
Ultimecia's Victory Pose and her EX Burst pose are the pose she takes before the final battle.
Her line when using Hell's Judgement, "absolute denial! End of existence.", is taken from her introduction in the final battle, "time shall compress. All existence denied."
Squall's line before fighting Cloud, "Talk is pointless for the both of us", references the fact that both of them are famous for being moody and not very talkative.
All of Zidane's Trance skills from the original game appear as attacks.
His intro to Shantotto is "if I win, you owe me a date", a reference to his bet with Garnet that she owes him a date if he wins the Festival of the Hunt.
When Zidane rescues Squall from Garland and Ultimecia, he says "Do I need a reason to help someone?" This is his signature line from Final Fantasy IX, appearing during one of the opening title cards as well as in-game.
After Kuja kidnaps him, Zidane escapes from Pandaemonium, the same place Garland imprisoned him in.
Zidane and Kuja both reference their game's version of Garland when facing him. Garland responds in kind.
Kuja's dialogue when someone other than Zidane confronts him in Shade Impulse, "I have nothing left to fear! But I refuse to die alone... You will all join me!", is what he says when defeated as Trance Kuja, "I won't have to be afraid anymore... but I'm not gonna die alone. You're all coming with me!"
Kuja's poem when Zidane confronts him is the same one he recited before attacking Alexandria.
Kuja's pose when using Ultima and ending his EX Burst is the same one he took when he destroyed Terra with Ultima.
All of Shantotto's HP attacks are "Ancient Magic", a special set of powerful spells that give the target an elemental weakness. The order Shantotto's spells chain — Fire -> Water -> Thunder -> Earth -> Wind -> Ice — is the order you'd cast them in in an ideal scenario, because the next spell in the chain is effective against the last.
When Shantotto loses, she turns into a doll, referring to an event battle where the player can duel Shantotto, but it turns out to be a doll she brought to life to fight in her place.
The AP needed to master Shantotto's Bravery attacks is in ascending order of the level you'd learn the spells in the original game.
All of Prishe's attacks are attacks from her original game, and the Skillchains resulting from her Bravery combos are the same Skillchains you'd get in XI from doing a combo with the same attacks.
Prishe's EX Burst refers to the five Mothercrystals, items the player has to collect to defeat Promethia. The shard of crystal she flings to end the EX Burst is the Star of Tavnazia, a magicite crystal she flings at Promethia to destroy it.
Prishe's quotes when using Nullifying Dropkick and EX Revenge are shortened quotes from when she uses Nullifying Dropkick and Auroral Uppercut in the original game — "you can't stop the tide of mortal existence!" to "you can't stop it!" and "time for a taste of knuckle sandwich a la Prishe!" to "knuckle sandwich a la Prishe!"
In the original Dissidia, when fighting Zidane, she asks if he is a Mithra due to his catlike appearance.
Each of Vaan's weapons appears identical to how it looked in the original game — his base weapons are the weakest equipment types of their classes, and his EX Mode weapons are the strongest.
Vaan and other characters mention his dream to own an airship and be a Sky Pirate.
Vaan randomly calls out "I'm Basch!" when using his EX Burst, referring to his infamous scene of running around Bhujerba calling himself Basch.
Sentence, Enrage, Lunge, Circle of Judgment, Guilt, and Innocence are all attacks Gabranth uses in his original two battles.
Gabranth's line to Shantotto "There is no future for the bystander. As there is naught he can defend" is based on what he says to Reddas, "Without power, what future can you claim? What good [is] a kingdom you cannot defend?"
Gabranth's calls of "Your life ends here!" and "By my sword!" are taken from his line when using Innocence, "your life ends at my blade!"
Gabranth's victory quote "even a stray has pride" is what he says when he attacked Vayne.
One of the Mognet chains of letters in 012 is about a helper girl from a shop who's missing. She got kidnapped by a group of Bangaas mouthing names like "Bal" and "Thier", but was later saved by a sky pirate. This is exactly what happened to Penelo in the original game.
All of Lightning's HP attacks are attacks either she or Odin use when she summons him. The button commands to input attacks in her EX Burst are the same commands used to attack in the original game.
The ability of Lightning's EX Mode to instantly Break opponents low on Bravery is based on the Omega Weapon's Quick Stagger ability, which staggers opponents once their stagger gauge is 90% full.
The name of Lightning's Manikin, Fleeting Flash, refers to her explanation of her choice of name, "Lightning. It flashes bright, then fades away."
The visual distortion that appears when using Army of One is the same graphic that Full ATB skills had originally.
Lightning's exclusive weapons reflect the weapon upgrade system of the original game — the Blazefire Saber is traded to buy the Flamberge, which is traded for the Omega Weapon; and the the Axis Blade trades for the Enkindler.
Her EX ability to nullify wall rush damage is a reference to the zero gravity device she uses in XIII to make long drops without injury.
Lightning's HP attacks scatter rose petals when they land. When Odin is summoned or transforms, rose petals are seen scattering as well.