Daggers, Darts, and other Throwables
There are few items better able to conjure up feelings of nostalgia for the Castlevania series than the classic weapons of the Belmont family clan. These are the weapons that our original hero, Simon Belmont had access to in the original adventure of the series. It's the true classics: Axe, Cross, Dagger, and Holy Water. Those, complimenting his primary weapon, the Vampire Killer, gave Simon all he needed to battle the forces of darkness, and they've been the stalwart standbys for the clan ever since.
What's interesting, though, is that for as long as the dagger has served as a standard part of the Belmont repertoire, it hasn't exactly been appreciated. Throughout it's run, the dagger is viewed as the "lesser" web-weapon of the series. The other weapons have their uses, bringing strength, power, and potential bonus hits for each attack, but the dagger has always been considered a consolation prize. "I don't have a sub-weapon, so I guess I'll take the dagger." Or, when it's accidentally picked up, replacing a better weapon, it's considered an actual curse. "Crap, I got the dagger."
And this has generally carried through the series. There have been minor upgrades brought in, and then set aside, in later games, but in general the dagger has remained the "also ran". A classic weapon that players rare want to get because its too weak, too under-powered, to actually be useful.
Daggers in Combat
As noted, the dagger has been in the series since the original Castlevania. Found in candles, or from random enemy drops, the dagger was a quick weapon to use. Thrown by hero Simon Belmont, the dagger would fly in a straight, horizontal line from the hero, all the way off screen. It wouldn't do a lot of damage, but it was quick and effective, especially against lesser enemies. And, as with all sub-weapons in the game, it could be upgraded with a double- or triple-shot, granting Simon the ability to throw multiple daggers at once (although, arguably, the triple-shot wasn't that effective as the dagger flew so quickly it was nearly impossible to get three out at the same time). And, of note, the dagger is called the "broadsword" in Vampire Killer, but otherwise functions the same as in Castlevania.
It was with the second game in the series, Castlevania II: Simon's Quest, that the dagger saw it's first upgrade. While the standard dagger can be purchased in Veros (for 50 Hearts), it is weak and not that effective, dealing low damage while only traveling across half the screen before disappearing. It's two upgrades, though, are much more useful. The Silver Knife, gained from a summoned Romani in Camilla Cemetery after Simon places a bit of garlic in the right spot, can travel the whole screen (not just half) and deals more damage. The Gold Knife, gained after battling Death in Brahm's Mansion, is even stronger, with the full effective range of the Silver Knife while also bursting into flames upon contact with a foe, dealing additional damage. For a casual player the Gold Knife can be great, but it's higher cost (consuming two hearts per use) and potential to add slowdown while its sprites are on screen, makes it far less useful in the speed-running community.
While the dagger in Castlevania III: Dracula's Curse is largely the same as that of the original game, there is one interesting twist. When playing as Grant DaNasty (in the Japanese version only), the pirate's primary attack won't just be a lunging stab with a knife but a toss of his dagger. This is a free use of the weapon, consuming no hearts, but he can only have a single dagger on screen. Equipping a second dagger in Grant's hands would allow him to have two knives on screen at a time, but the second would use up a heart of ammo.
From here, the dagger is basically gained, and used, as you would expect in all the later games of the series (in which it is featured). It's fast, it's weak, and it travels the whole screen. However, Castlevania Dracula X: Rondo of Blood introduced another recurring twist: item crashes. Hero Richter Belmont could overcharge his sub-weapon, performing devastating attacks. With the dagger in hand he could throw multiple daggers at one (a skill which, in Castlevania: Portrait of Ruin was dubbed "1,000 Blades"), creating a horizontal flurry of poking damage. This could be effective against a few bosses, including the Bat Company, finally giving the dagger some real effectiveness (but only when it could be crashed).
Other Thrown Weapons:
In later games other thrown weapons were added into the mix. Castlevania: Symphony of the Night was the first to bring in more thrown weapons, creating an entire class of consumable items for hero Alucard to toss around. These included the Shuriken, Cross Shuriken, Buffalo Star, and Flame Star, all of which traveled horizontally (like a dagger) while dealing potent damage against the enemies. In fact, with a Duplicator in hand, Alucard could throw such a fury of Buffalo Stars that even most bosses would die in but a few seconds.
The Shuriken appeared again in Castlevania: Curse of Darkness, wielded by hero Hector on his quest (after the hero forged it). It then came back again as one of the many sub-weapons for Johnathan Morris. While the basic shuriken was actually thrown in pairs in a short arc, the more powerful Yagyu Shuriken took on the standard, dagger-like behavior while, once more, dealing potent damage to foes.
And then there was the dart, another sub-weapon for Johnathan. This one could be purchased early in Portrait of Ruin, and it would travel like a dagger, horizontally across the screen. When it hit it would create a faint dart board on the enemy, a silly little flair for a weak weapon. It could be mastered though, which would up its damage some. It's most important use, though, wasn't as a weapon but as part of weapon-dashing, the act of throwing and then canceling a weapon with a dash to move quickly backwards. This is a technique used by some speed-runners in the early part of the game to gain quick movement (before other options become available).