The Double Hammers and Weapon Masters in the bonus areas are most notable. They move fast, hit hard and can hit you from across the screen. Your first fight with them will probably lead to death from offscreen.
Tin Men are an example encountered in the course of normal gameplay. You can summon one in the last part of Minera Prison Island by stepping into a spotlight (at this point, it's pretty much a Boss in Mook Clothing, and only a very skilled — or overleveled — player will be able to defeat it). When you encounter them again in Dracula's castle, they're STILL a major threat.
Also, Cave Trolls. You can first encounter them in the second part of the Tymeo Mountains, which is fairly early in the game. They're still dangerous when you encounter them in the castle.
Fan Nickname: A variation. Before the game was released, Brachyura was known as Blacula due to a fan's mistranslation.
This game gets the moniker of being the Metroid: Fusion of the series, due to the linearity.
More specifically, both games are divided into several small areas which are visited in a specific order according to objectives given to by a male NPC (Samus's AI partner and Barlowe) rather than being one large, interconnected world, the main characters start out far weaker than usual for their respective series, making bosses and enemies considerably tough, and both Fusion!Samus and Shanoa gain new abilities by absorbing something taken from their fallen enemies (X-parasites and glyphs).
Game-Breaker: Nitesco combined with any weapon creates a giant sword that can hit nearly anything on the screen. Its light elemental makes it extremely strong against most enemies (and its fire elemental does at least decent damage to most enemies that resist light), and it gets stronger every time you use it. Add on the Death ring (or two), plus Dominus Agony, and you can destroy ANYTHING that doesn't absorb light or fire elemental attacks.
Nitesco itself. Think the Crissaegrim, except you can just steal it off a regular enemy trying to cast it, no incredibly rare random drops needed. You can't get it until partway through the castle proper, though, which at least limits the amount of time you can abuse it on your first playthrough. Conveniently, however, your first opportunity to get it comes right before Blackmore, and it just so happens that he is weak against Light attacks.
The Queen of Hearts helmet. Not only does it offer some of the best stats of any helmet in the game, it halves the heart-consumption of all special attacks. Normally, you'd have to complete Hard Mode with a level cap of either 50 or 1 to get it... or you could just get a copy of Castlevania: Judgment on the Wii and sync with it, giving you the helmet right from the start.
To a lesser extent, the food items unlocked through Aeon's quests. In previous entries, the only healing items available to buy were potions (and the occasional Powdered Milk), which meant the player would have to farm for food items if they wanted more healing. In this game, the food items are plentiful and can be unlocked early (Aeon can be rescued immediately after you acquire the double jump, in fact—and the first two quests can be done at that time too). Some of the food items you can unlock are quite powerful, and all of the unlockable food items are much cheaper than potions of equivalent power would benote For example, both the Ramen Noodles and the High Potion heal 200 HP, but the Ramen Noodles cost 800 gold while the High Potion costs 2000. A less-than-stellar player can potentially tank their way through difficult encounters by using their massive supply of store-bought food to heal up.
Quite a few enemies, especially later in the game.
An early example being the Skull Spiders on Hard Mode (without the bonuses of NG+).
Goddamned Boss: Brachyura on a New Game+, as he's the only boss you can't just speed through with your previous-playthrough Glyphs and stats; you're still forced to tough out the entire fixed-pace tower climb. He escalates into That One Boss territory if you're trying to get his medal.
Harsher in Hindsight: During the tutorial, Barlowe says "So armed, you can wield Glyphs against your foes. Imagine I am one of them, and strike!" Guess what happens later in the game...
Les Yay: Two female villagers constantly flirt with Shanoa, and the Werebat enemy will joyfully exclaim "Let's play, cute little kitty!" every time one sees her.note which can be a CMOF if she's using the Cat Girl glyph One of the female villagers, in particular, is all but explicitly in love with Shanoa. She even makes her a wedding dress.
Relationship Writing Fumble: Shanoa and Albus are supposed to be seen as Like Brother and Sister, but some of Albus' dialogue sounds more like what a lover would say. It doesn't help that we don't see much of Shanoa prior to her memory loss, which could've helped clear the confusion a bit.
Tear Jerker: The ending, where Shanoa smiles for Albus, who sacrifices his life.
That One Attack: Dracula's bat swarm in his second phase. It ignores Mercy Invincibility, it takes fairly precise positioning to avoid, and it can shred away your entire health bar almost before you can react. It only takes a few seconds of this to go from full health to Game Over.
Blackmore fills the screen with projectiles and attacks that will kill you in about 4 hits. Unless you bring enough dark resistance and light glyphs, you better hope you're good at dodging. There is a very good reason why you're provided the opportunity to grab the Nitesco glyph literally just before you confront him.
Also, Eligor, a giant mecha centaur knight which you have to be very used to its patterns to beat easily, especially when you're on its back.
Earlier on there's Gravedorcus. There's barely any room to maneuver in and, due to the boss's movement patterns through the floor and his resilience to everything but ice, you'll be stuck with Vol Grando the entire fight, making him surprisingly durable.
Ruvas Forest, one of the game's "straight line from point A to point B" sections. On normal, it won't be too bad... on hard, with a level cap of 1, however, it will absolutely destroy you. Observe. You'll need a lot of jumping, a lot of health items, and a lot of luck.
The Hard Mode version of the Skeleton Cave in a fresh New Game is unpleasant, too. Sure, you get Vol Macir (a blunt weapon) dropped in your lap shortly beforehand, but it's not of much consolation. The place now contains a Blade Master, a very fast enemy you'll be very hard pressed to defeat withourt bashing it with a glyph union at least once, and drastically buffed Bone Pillars that can shoot fire at an unreasonable rate, and the only Scutum glyph you have at this point is useless, as it doesn't cover your front side. You basically have four options for dealing with them. One is to charge and take a ton of damage, probably dying in the process (not recommended). The second is to destroy them using Glyph Unions, and this wastes your precious hearts. Three is to chip them to death from the edge of the screen with Culter, Arcus, Grando, or Umbra, all of which take an eternity due to all of them being a type that the Bone Pillars resist. Luminatio can't be used for the first stack because it simply does not reach, and the second stack is positioned in such a way they're inevitably going to shoot at you several times before you can get away, not to mention yet another stack being to the left anyway. The final, ideal way requires you to think outside the box. Return to the Monastery with Luminatio and Umbra, and go to the falling blocks room. Destroy them with the Light/Dark union, and absorb the Cubus glyph. While it seems completely useless at first glance, the important part is that the Bone Pillars' fireballs cannot pass through it, so you can use it to protect yourself while you inch forward (staying crouched for the most part so the middle pillars' shot goes over your head), dropping more cubes until you're close enough enough to bash them with Vol Macir. Repeat for the second stack of three, destroy the block beneath you with Luminatio, and repeat Cubus a final time for the last stack. Even that is a little slow, and carries the risk of getting hit in the face. At the very least, Maneater (the boss) remains rather pathetic, and can be put down without significant trouble, as well as the place's sole save point being at his boss door.
They Changed It, Now It Sucks: Quite a few people were upset with the shift from exploration to combat. Even when the fanbase warmed up to it, the most common criticism is the linear level design.
They Wasted a Perfectly Good Plot: Albus Mode could've been an entirely alternate stoyline a la Julius Mode, wherein Albus decides that he'll take on Dracula instead of Shanoa (since that seems to have been his driving motivation to begin with), and the battle with possessed Albus is fought against Shanoa instead, but all it amounts to is a Self-Imposed Challenge.
Vindicated by History: While not exactly hated at its release, the game has gotten an ever-warmer reception as the years pass. The numerous attempts to shake up the formula, having a main female protagonist, a refinement of the Soul system, and a higher degree of challenge have put it for many as the best DS entry in the series, if not one of the best Metroidvanias in the series, period.
Win Back the Crowd: This game includes many linear, enemy-dense areas with distinct patterns, high damage, and a variety of weapons to appeal to Classicvania fans. It largely worked, while still providing enough secrets, backtracking, and exploration in the latter half to satisfy the metroidvania crowd.
The Woobie: Shanoa. She got manipulated into resurrecting Dracula by none other than the man who raised her, who also stole her memories and emotions.