"Vampiric Orchis" and "Vampiric Koala" are not "Vampire" cards because they do not have 「ヴァンパイア」 in their Japanese names. Also, their Attributes are EARTH, not DARK, which most Vampire support requires (except "Vampire Vamp"). In the Italian version, the inclusion of cards whose names contain the feminine word "Vampira" (e.g. "Vamp Vampira") and the plural word "Vampiri" (e.g. "Regno dei Vampiri") seems to be implicit, because their names don't contain "Vampiro".
"Vampire" monsters typically resemble pale-skinned humanoids with irregularly colored hair (white, green, etc.) in mostly aristocratic clothing resembling that of the 18th to 19th century, evocative of the common depiction as the mythological undead creature of Europe, and with them being tied in infamous legend to tyrannical and corrupt nobility. Many Vampire monsters have claw-like appendages on their clothing, best seen in the artworks of "Vampire Sorcerer" and "Vampire Vamp. Some of the monsters also bear resemblance on vampire characters from other franchises.
"Vampires" later obtained new support revolving around paying Life Points as costs to Special Summon themselves from the Graveyard and search other "Vampire" cards while also taking control of the opponent's monsters, often by Special Summoning opposing Monsters that were destroyed by battle with a "Vampire". This also facilitates the Xyz Summon of "Damphir Vampire Sheridan" as it can treat monsters the player controls that are owned by the opponent as Level 6 when used for its Xyz summoning. The Life Point costs can then be recovered with the use of "Vampire's Domain".
"Vampire Sorcerer" is very helpful for both of the Deck's goals. Its first effect allows you to search any DARK "Vampire" monster or any "Vampire" Spell/Trap Card, and its second effect allows you to Normal Summon one "Vampire" monster without Tributing. You can use its first effect to search for "Vampire Kingdom" and its second to Summon "Vampire Lord" or "Vampire Grace" in order to mill your opponent, or you could search for "Shadow Vampire" and use the second effect to Normal Summon it, use the effect "Shadow" to Special Summon "Vampire Lord", and Overlay for a DARK Rank 5.
While "Vampires" are fairly powerful in controlling your opponent's Deck, they can be devastated by their own effects too. Opponents who know that you use "Vampire"s, or during Duels 2 and 3, will be likely to side cards like "Dimension Fortress Weapon", "Skull Invitation", "Breakthrough Skill" or even "Jackpot 7", with the last one being most dangerous due to "Vampire Kingdom"'s effect being compulsory. Decks that utilize the Graveyard as resource are also problem as well, for the same reason. "Lightsworn" Decks in particular can take huge advantage of a "Vampire" player, while Decks such as Zombies and "Infernities" that can construct huge combos out of the Graveyard pose a similar threat. A lone "Vampire Hunter" can potentially destroy an opposing "Vampire"-centered deck, especially since all "Vampire" monsters are DARK.