As indicated in the Celebration setting post, vampires are about to become a thing again. As such, a want to go over some of the basics with you, so that you will be able to plot with and NPC them for yourself during the masquerade event.
The vampires that the carnival has been having trouble with are of a demonic variety - a new vampire is created by infecting the freshly dead or dying body of a victim with the blood of their vampiric killer. This is accomplished by drinking from them, and then orally feeding them your vampire blood. This will infect them with the vampire curse, fully killing the victim and then resurrecting them unto a kind of undeath, that is not quite living and not quite dead. Any creature with blood is capable of being given this infection - but it has to be something that actually serves as blood, and not just oil or fuel. Most robots or inorganic creatures will be excluded, with a few possible exceptions.
Once transmitted, the infection corrupts the soul of the victim with demonic energies - something almost like a possession, from a second spirit that they will come to know as their "beast." This demonic beast spirit will fuse with the victims, and though it is possible to separate them after the fact, it is magically rather difficult. This demonic spirit contains most of what one would consider to be vampiric instincts - the lust for blood, animalistic tendencies, and a violent nature. It can be combated against by the host, but how much success they will have depends on the strength of their own spirit.
A vampire's power increases as they age, marked by the advancement of their demonic infection. A new vampire will be far less powerful than an elder vampire. As they develop, they will gain new abilities while still retaining their old ones.
A freshly made vampire - that is, still within the first year or two of their undeath. Neonates are the most numerous stage of vampire, as whether or not they survive this stage tends to be a right of passage towards becoming a full adult. While a terrifying enemy against regular mortals, those with strong magic or enhanced combat abilities will find it possible to take them one on one, or even one on two if they are feeling spry. About 80% of the vampires that attacked the carnival months ago were neonates. Neonates tend to be less graceful than adults, and also struggle to control their bloodlust. Neonates will be available for anyone to NPC during the masquerade.
Physical Power: A neonate vampire could lift a half-ton truck, and can move with speed just beyond peak human physical capability.
Supernatural Charm: New vampires immediately begin to exude a kind of animal magnetism, that will subconsciously draw in humans and other like-minded creatures. Those near them will find it difficult to say no to their demands, and will find it tempting to get close to them, due to a mixture of intimidation and seduction. They may or may not realize that this is an irrational compulsion.
Paralytic Saliva: Their saliva can cause numbness in areas touched by it, as well as causing victims to lose control of their motor functions with prolonged exposure. This is a magical affect and not a chemical one, so it will work on any creature that would be susceptible to alchemy based poisons.
A fully matured vampire, this stage will have developed additional powers and physical capabilities, and will gradually grow in strength with them as they age. Depending on a vampire's sire, it may take anywhere from a couple months to a few years to reach the state of being fully mature. This means that an "adult" vampire could have been undead for anywhere from a few months to a few centuries. The remaining 20% of attackers were mostly adult vampires. Adults can be NPC'd by players during the masquerade, but only if get permission from the mods first and give us an idea of what they'll be doing, so we can keep track.
Physical Power: By the time they are an adult, a mature vampire's strength and speed will have approximately doubled from how they were when they were a neonate. That means about 1 ton lifting strength and the ability to move twice as fast as any human.
Hypnosis: At this stage, vampires will have learned how to use their magnetism to fully hypnotize susceptible victims, based primarily on the use of eye contract and voice. Though outside interruption can break the hypnotic trance, while in its sway a vampire can use it to control or break down a victim's will or even convince them to forget or missremember information. With enough time and exposure, a victim's memory and identity could be completely warped by this power.
Beast Control: Vampires can use their own "beastial spirit" to control or intimidate animals. Predators and scavengers will be inclined to obey their will as if a member of their "pack" and prey animals will be instinctively terrified of them. This effect may work on those in the carnival with animal instincts, whether they be from fae effects, a part of their species, or otherwise.
Shadowalk: Not quite teleportation, not quite invisibility - vampires can blend into the shadows and pass through crowds without drawing attention. If there is any shade present, they will be able to blend into it and go unseen by human eyes. In crowds, this will make them completely indistinct to people's notice - they may realize there is a body there, but its relevance will be completely suppressed until they strike.
The longest lived of all vampires, elders are usually at least a thousand years old if not older. They are the most loyal servants and right hand men of their demonic overlord, and can bend the wills of most mortals with ease. Elders are not available to be NPC'd by players, and will be exclusively under mod control for plotting purposes.
Physical Power: This is where you get to the level of being able to shove semi-trucks around and moving so quickly it may as well be teleportation. Wounds will heal within minutes if they haven't been dealt by silver or holy magic. Damaging the heart can prove to be difficult, as even getting through an elder's outer skin is a challenge. Elders are also more or less immune to damage from heat or cold.
Mind Control: Straight up mind control, without the fragility or hypnosis. Elders can erode the will of humans just by being around them, and can control multiple individuals at once, to varying degrees.
Transformation: Elders can turn onto smoke, thus becoming mostly immune to damage, and can also grow bat wings and other devilish features at will.
All stages of vampire are vulnerable to silver, particular forms of holy magic, and damage done directly to their heart. They are not more vulnerable to fire than average. Most other injuries can be healed within days or even hours, provided they are able to feed and recover. Destroying a vampire's heart will destroy the demonic spirit's hold on their body, thus effectively killing them.
BECOMING A VAMPIRE↴
Since the villains of this plot are vampires, there is going to be the potential for carnival members to be turned into one during the attack - provided they have the necessary blood, of course. This transformation will not necessarily be permanent, as the Ringmaster will be capable of potentially removing the infection with enough time and care, and so your character could be expected to be in that state for as little as a week, or up to as long as 'indefinitely', depending on your narrative preferences. That is, after things have been settled and they have been brought back to the carnival in one piece.
Being turned into a vampire will mostly occur during the masquerade, during which vampires will be using stealth and seduction to turn or capture members of the carnival. The primary focus of kidnappings will be on the supervisors, or order to most effectively disorganize the carnival's ranks, but being turned could happen to just about anyone. Once a character is turned, they will be compelled to obey their sire, and follow the bidding of the vampire's overlord - this effect will last until these characters are subdued or rescued from the vampire's clutches. Special situations asides, all captives and newly turned vampires will be stolen back to the vampire's home dimension before the masquerade is over.
New vampires will, by default, start with the abilities of a neonate - however, if they are turned by a particularly old or or elder vampire, they will potentially get a head start on developing adult vampire abilities. The older the vampire the sire, the more powerful their progeny will be. The purpose of turning carnival members is mostly to corrupt and confuse their command structure, and also to be as huge of dicks as possible.