A giant rotting corpse hanging by massive hooks, and supported by flies the size of minivans. Symphony of the Night is AWESOME!!!
Dracula keeps reviving, and the Belmont family and their allies keep sending him back whence he came. Along the way, they have had many awesome boss fights.
Dracula basically makes it his job to come up with a more awesome transformation every game. Here's some that stand out:
Curse Of Darkness: A winged demon so big, you literally are barely the size of a FINGER to him.
Dracula's Curse: Your first fight him as himself, he switches into a giant, floating, disembodied, many-faced BRAIN (that drips acid, to boot!), and finally a huge laser-spewing demon.
Bloodlines: First his basic form, then a sort of fireball-throwing magician, and then a demon with a face on his torso, Devilman-style. This "second form" isn't actually Drac; it's really his Wicked WitchDragon (well, for Bloodlines, anyway). The English version erroneously labeled this separate character as Dracula. Same thing in that game with the Dark Lord's niece, Elizabeth Bartley, who summons Medusa but doesn't actually become her.
And just when fans are getting bored with this, Order of Ecclesia gives us a Dracula who, after being defeated, simply shrugs it off and starts simply walking towards you instead of standing in one place, occasionally teleporting like most encounters. This version of Dracula is easily the scariest. He doesn't need some giant bat form! HE WILL CALMLY WALK OVER TO YOU AND PIMPSLAP YOUR FACE OFF. And if you try to jump over him, he'll pimpslap you. If you try to fly, he'll pimplazerslap you.
Oh and Portrait of Ruin. "Boy, Dracula sure will be much easier since I have two characters to fight him this ti-... DEATH? AT THE ... SAME... TIME...." Made even more awesome by the fact that, like you, they have several Combination Attacks and, when one of them's low on health, Death lets Dracula use Soul Steal on him, resulting in a fusion of the two. Even better; they have Combination Attacks, including a version of Dracula's hellishly destructive Demonic Meggido where Drac turns Death into a scythe and slams him into the ground, creating a massive wave of ruination. Holy...
Both the Dracula fights in Mirror of Fate are awesome, though the first gets special mention for featuring Alucard and Simon double teaming Dracula. It's as awesome as it sounds.
If you don't cheese him out with a certain subweapon, the second Doppelganger fight is pretty freakin' intense. For even more fun, get rid of your cloak and familiar so that you're a perfect visual match.
Galamoth, probably the most difficult battle in the game, but very satisfying if you don't use Game Breaker methods.
Richter Belmont. For the first time in the series, you're fighting against a Belmont, and he has all of the moves he would have if you were fighting as him - and is not afraid to use them!
Beelzebub. Just read the caption on the page image.
This game's version of Legion, a grotesque orb of flesh made up of bodies. As you attack the Legion, the bodies fall off and rise up to attack you, which is quite graphically stunning. When you attack it enough, you see the core of the Legion, which has tentacles around it that shoot lasers.
Julius Belmont in the good ending. He knows every single Belmont trick, does not hesitate to use said tricks, and is nightmarishly difficult—and then starts using subweapons! Far more satisfying than the final boss. And he has awesometheme music.
And look closely when he's performing Grand Cross. The might of the attack is so powerful that it not only draws in Soma like a mini black hole, but when unleashed, it causes the castle in the background to start crumbling.
And the dialogue after the fight implies he was holding himself back the whole time.
Fighting, of all things, Chaos in the true ending.
In that same vein, Graham has the same effect.
Balore. You enter the boss room in the arena level and is greeted by the Giant Bat, a standard boss in Castlevania. Suddenly a GIANT HAND comes out of nowhere and crushes the bat, and an Evil Laugh is heard as Balore fades in from the background while a different boss battle music starts to play. Totally unexpected and an epic boss battle.
The Puppet Master, a giant wooden marionette head with four arms, constantly spitting small dolls at your, or creating a doll and trying to slam it in an Iron Maiden, at which point you switch places with the doll. Ouch.
Bat Company. A twist on the usual "bunch of little bats join to form one big bat" in which the group of bats are still a group of bats, and change shape constantly. Fitting that it's fought in a throwback level that's a homage to the original Castlevania, where the boss was a giant bat.
Gergoth. A giant mutant dinosaur like boss, that slowly plods around the top of the Condemned Tower, jumping, shooting lasers, and blasting poison gas. Halfway through the battle, it smashes through the floor of the tower, and you fall all the way back to the ground floor where you started the level. And NOW it's gained speed!
Paranoia. A harlequin demon that flits in and out of the giant mirror in the background, while shooting at you from the mirrors on the sides of the arena. And when you do defeat it, it turns out you just fought its reflection, and the REAL boss fight starts up next room!
Abaddon. A demonic conductor who orchestrates swarms of locusts to attack you.
Dark Lord Soma in Julius Mode is pure, classic Dracula. And the fight is accompanied by Illusionary Dance.
Except he surprises you by pulling out a Gaibon familiar and Great Axe Armor's attack rather than Dracula's traditional fireballs. Then when he transforms into the monster from Rondo of Blood/Symphony of the Night, he gets a Harpy familiar, then will use Aguni, Larva and Abbadon.
Zephyr from the Clock Tower. You are facing none other than Castlevania's answer to Dio Brando.
Albus, who is probably the only guy in the series besides Soma to use a gun, making this fight unique and interesting. In fact, it gets even better when you fight him as Albus... And the boss uses the same quotes, which make it hilarious when you realise he's addressing the wrong person, but when you discover that the flaming kick attack is his weakness, flaming kick duels ensue. Think Sanji fighting himself with his legs on fire. Awesome.
The Giant Enemy Crab should deserve a mention — how many other games let you smash a crab with an elevator? Coupled with that boss being a major Wake-Up Call Boss to a degree, it makes the ending soooo much more satisfying.
What Shanoa says makes that ending even MORE satisfying. "Go to hell."
Eligor deserves a spot here. It's a Giant Robot Centaur Demon with a giant sword and ballistae on its hips. Giant as in several stories tall. The fight is a Colossus Climb of epic proportions where you have to take out the knees and ballistae before you go for the head while it very effectively tries to swat you off. Also, it is hard. Really hard.
Blackmore. This guy greets you smarmily, before fighting you with his own gigantic shadow. And this shadow is shaped like a wolf. Blackmore controlls the wolf-shadow by dancing and likes to use this big black laser move on you. By now you have Nitesco, a very effective glyph that also manifests as a laser. Mega-awesome laser fight ensues.
The fight with Rusalka is awesome, especially considering the huge waves she uses to attack.
The fight with Brauner. Mostly for his overly dramaticattack-calling. "A painting of the SOUL!" "THIS is ART!" "I'll make YOU my masterpiece!" And so on...
Fighting the Whip's Memory, aka the essence of Richter Belmont inside of the Vampire Killer. Little breathing room. Jonathan only. The boss can and will hand your ass, but it's a wildly satisfying battle from start to finish. And just imagine if it was the real Richter, who was widely touted as the greatest of the Belmonts.The music(a remix of "Divine Bloodlines", which is more or less Richter's theme) only plays up the intensity of the fight.
Made even better when you realize what his weakness is: The Cream Pie, a hidden subweapon found all the way back in the first painting. The Memory is weak to the darkness element, which the Cream Pie inexplicably has. The Pie also has the benefit of being extremely light on MP consumption. The result is that one of the easiest ways to beat the Memory is to throw infinite amounts of pie at him until he dies.
The fight against the Black Knight, a large warrior-Golem who is royally pissed off with Gabriel. His attacks are surprisingly fast and do quite a bit of damage, so this is pretty much the first fight that demands you make good use of the Light/Shadow/Focus cycle, and it is cool.
The first Lord Of Shadow: Cornell, Warrior-King Of The Lycans. In the first stage, he is quite tough with quick movements and deadly swings of his war-hammer. But at the second stage of the fight, he transforms into his monstruous Lycan form, and is now very fast and very tough. You will likely die a few times to him, but the almost dance-like way you have to dodge his attacks before countering them is very fun. The way you finish him is really satisfying as well.
The battle against The Titan in the Lords of Shadow 2 demo. Climbing The Titan as the eponymous music plays is pure awesome.
The final battle against Dracula in both Alucard's and Trevor's routes of Mirror of Fate. The music seems to accent your attacks perfectly, and Dracula himself is on the perfect level of Challenging VS Impossible.