Bat Transformation Relics
Because Alucard -- in addition to being Dracula's curiously named son -- is a vampire just like his dear old dad, it should come as little shock that he can gain the power to transform into a bat -- also just like dear old dad. The "Soul of Bat" relic -- found in the "Long Library" section of the game -- confers this transformation power to Alucard, while the "Fire of Bat,' "Echo of Bat" and "Force Echo" relics grant Alucard fireball powers, radar powers and radar wave attacks respectively while in bat form.
Wolf Transformation Relics
While it may seem a touch strange that a vampire would be able to transform into a wolf -- that's more of a "Werewolf" thing, after all -- "Symphony of the Night" ignores that little gap in logic and grants just such a power to Alucard through the appropriate relics. "Soul of Wolf" allows the transformation, while "Power of Wolf" and "Skill of Wolf" convey added speed and a special attack respectively as long as Alucard is transformed.
Mist Transformation Relics
The third transformation power is more in keeping with Alucard's vampiric origins -- Vampire lore provides several examples of the toothy villains transforming into vapor when needed -- and allows him to transform his body into near-invulnerable mist for a short amount of time. "Form of Mist" is the transformation relic, while "Power of Mist" and "Gas Cloud" allow Alucard to remain transformed longer and to transform into a damage-dealing poisonous cloud, respectively.
Useful Item Relics
More of a "Grab Bag" of relics, these are relics Alucard will come across that will have a minor effect either on himself or on the environment. The "Cube of Zoe" will reveal hidden items, the "Spirit Orb" reveals enemy health, and "Gravity Boots" grant extra jumping power to Alucard. The "Leap Stone" allows Alucard to double-jump, the "Holy Symbol" -- ironically shaped like a snorkel -- allows Alucard to survive under water, and the "Faerie Scroll" displays the name of Alucard's enemies on screen. Lastly, the "Jewel of Open" and the "Merman Statue" allow Alucard to open locked blue doors and summon the Oarsman nonplayer character, respectively.
Familiar Card Relics
When Alucard finds a Familiar card along the course of his adventures, he will gain the power to summon a specific type of familiar to fight alongside him for a time. The types of familiars he can find and summon are "Bat," "Faerie," "Ghost," "Demon" and "Sword."
Bits of Vlad Relics
Harking back to the earlier "Castlevania: Simon's Quest" game, Alucard must collect the five scattered pieces of Dracula -- who's first name is, apparently, Vlad -- in order to open the Ceremonial Chamber room in the Reverse castle. Vlad's body parts, in addition to being incredibly morbid keys, also convey added bonuses to Simon every time he finds one. The "Heart of Vlad" renders Alucard immune to curses, while the "Tooth," "Rib," "Ring" and "Eye" of Vlad grant a plus-10 to Alucard's strength, constitution, intelligence and luck scores, respectively.