Bat Form

Alucard and Soma Cruz can take the form of a bat in many games. Alucard naturally possesses this ability, being a dhampir, while Soma eventually develops it thanks to his power of dominance over souls.

Castlevania III: Dracula's Curse
Alucard is able to transform into a bat in Dracula's Curse at any time by pressing ↓ and [JUMP] at the same time. Flying around as a bat allows him to avoid obstacles but consumes Hearts at a steady rate. Being hit by an enemy while in bat form will cause him to revert to human form. This is especially dangerous, as this ability is generally used to fly over big "bottomless" chasms which, if hit in midair, usually means instant death as Alucard will helplessly plummet down to his death.

Castlevania: Symphony of the Night
In Symphony of the Night, Alucard is able to turn into a bat once he finds the Soul of Bat relic. While in bat form, he will normally fly at a slow speed while consuming MP. The powerful Wing Smash, which causes his bat form to dash across the screen at high velocity while dealing out damage, can be pulled off if the player knows the button combination (hold [JUMP] + ↑↖←↙↓↘→, release [JUMP]). The Wing Smash ability varies depending on the version of the game. In the PlayStation version and ports, it has a fixed duration and Alucard will automatically leave bat form after a short dash. The dash can be extended by re-inputting the command for the spell during the previous one, allowing a Wing Smash to continue until Alucard either, hits something or runs out of MP. In the Saturn version, the Wing Smash won't automatically end and will continue for as long as Alucard doesn't hit something or runs out of MP.

Alucard can gain additional abilities for his bat form by gaining additional relics, including:
 * Fire of Bat: This relic allows him to shoot fireballs while in bat form.
 * Echo of Bat: This relic gives him a sonar which will allow him to see what is ahead in dark areas.
 * Force of Echo: This relic causes his sonar to deal damage.

If the Bat Familiar is out while in bat form, it will mistake him for a possible mate and a heart will appear over its head. Smitten, it will follow him much more closely, making it more useful. Also, additional bats will be summoned depending on the familiar's level (one additional bat for every 20 or so levels). If the Fire of Bat relic has been found, whenever Alucard fires off a fireball while in bat form, any bat familiars following him will launch a fireball as well. The bat familiar has no action to match the Wing Smash ability, however.

The color of the currently equipped cloak, as well as the customizable Joseph's Cloak, affects the color scheme that Alucard's bat form will take.

Castlevania: Aria of Sorrow
Soma Cruz can also take the form of a bat in Aria of Sorrow, where he can activate the Giant Bat's soul to do this. While in bat form, equipping the Flame Demon's soul (Hellfire) and the Succubus' soul (Death Touch), allows him to shoot fireballs; equipping the Bat's soul (Echo of Bat) allows him to use this ability; equipping the Blue Crow's soul allows him to summon crows in rapid succession (although the limit of the soul is still considered).

Throughout the game, Soma can find three ancient books, each of which give a hint about a particular soul combination that has to be used at the Top Floor. Ancient Book 2 says: "The second spirit is the King of Bats."; if all three correct souls are equipped while dealing the last blow to Graham's first form, Soma will then be able to confront his second form, eventually accepting his condition as the reincarnation of Dracula; then the good ending become available to the player.

Castlevania: Dawn of Sorrow
In Dawn of Sorrow, Soma can transform into a bat by activating the Bat Company's soul. Equipping the Flame Demon's soul (Flame Ball) allows him to shoot fireballs while in bat form. Soma is also able to summon a Fleaman while in bat form by activating the Fleaman's soul (Hopping Man).

Alucard could take the form of a bat in Dawn of Sorrow by selecting it as a sub-weapon.

Castlevania: Portrait of Ruin
In Portrait of Ruin, instead of a bat, Charlotte Aulin can change (or make Jonathan change) into an owl by casting the Owl Morph spell to fly around, which is essentially the same as changing into bat form in previous titles, although no extra abilities can be acquired for this form other than just flying to access hard to reach areas.

Castlevania: Judgment
In Judgment, Alucard is not seen actually taking the form of a bat. However, bat wings sprout on him while he performs the Wing Smash dashing-slash move, and during his Infernal Blade finishing move.

Trivia

 * In Symphony of the Night, the "tail-like" formation which the bat familiars take when following Alucard while in bat form, is reminiscent of how Options follow the player's ship in the Gradius series and its spinoffs.