Unique Enemies in Castlevania.
- Castlevania: Aria of Sorrow has a couple of ordinary enemies who appear in just one room to frustrate 100% Completion, such as the super-fast flying fish enemy that requires a TimeStopper from another Unique Enemy, the Chronomage, who functions as a Broken Bridge. There's also the almost harmless Tsuchinoko enemy, which is an in-joke on a Japanese cryptid/urban legend found in an otherwise empty room after a boss battle early in the game which you'd never revisit without specifically looking this monster up.
- Castlevania: Dawn of Sorrow also has a few unique enemies. Three are of the "special requirement to find" (Mothman, Winged Humanoid and Yeti) variety, and there are several others that just happen to have one spawn location in the entire game (such as the Alura Une and the Wakwak Tree).
- Castlevania: Symphony of the Night:
- The Dodo bird, who appears in one room and runs for its life the moment it sees you...with good reason, too, as killing it gives you a chance at an Infinity +1 Sword drop.
- Symphony actually has loads, especially if you consider enemies that appear more than once, but never outside of the one room they're found in.
- The Mud Man is only summoned by the Lesser Demon in his Boss Battle. When he returns as a Degraded Boss later in the game, they summon other Lesser Demons. This also makes it a minor example of Permanently missable content, as if you beat the Lesser Demon before they summon any Mud Men, you cannot complete the enemy list in the library.
- The dodo above re-appears in Portrait of Ruin in a single room... sometimes. It's pretty much random. There are also a few others. Sand Worms in the desert levels only appear once and never re-appear once killed, and there are two palette swapped kinds. A ghoul king only appears after killing ghouls in certain rooms after a certain time, and the giant ghost only appears in a single room after killing ghosts for a certain time. Aside from the sandworms, they're required for sidequests.
- Oddly, the Stone Rose/Man-eating Plant which is fairly common in later games only appears in one spot in Stage 1 of Castlevania: Rondo of Blood (and in a room off of the side of the alternate path rather than the main one, to boot), as well as the hunchback in Stage 3 who tries to steal your subweapon.
- The glass skeletons only appear in one room in Castlevania: Harmony of Dissonance. They seem to be there to give nice exp. Also, the aptly-named Rare Ghost, which only has a 20% chance of appearing in one of a few rooms. It is entirely possible to go through the game without even seeing one. There's also a number of unique Armor enemy variants that only appear in a single room. One enemy, called the O, appears in only one room in the entire game and swipes your sub weapon if it manages to touch you. Letting it succeed is the only way to unequip your sub weapon and thus use Juste's healing spell.
- Devil in Castlevania: Circle of the Moon, an absolutely vicious Boss in Mook Clothing that can drop the best healing item in the game, is found only at the top of the Observation Tower and in the final room of The Arena.
- After beating certain bosses, certain earlier rooms add variant enemies with rare, unique drops. These include the three candle mimics and lady bats which take up residence in defeated boss rooms and out-of-the-way regions
