The power you were talking about is Shadow Occultism
-In order to utilize Shadow Occultism the practitioner must possess Obtenebration 5, Occult 5 and the specialty Abyss. There are two rituals that can be researched using Occult Influence. These are described below.
Summon Abyssal Creature
-This requires a successful Occult 4 Influence action to research and is considered an Intermediate Ritual - costs 4xp to learn.
This ritual takes one hour to perform. During this time the caster must spend one blood point and win a static Mental Challenge against 7 traits. If the ritual is successful the caster then summons a single Arm of the Abyss. It has all the normal attributes typical to the Arm plus one Mental trait per level of Obtenebration possessed by the caster. The summoner can choose the exact traits. Additionally the summoner can sacrifice his own Mental traits to increase the Mental traits of the abyssal creature. Each additional blood point spent in the summoning of the Arm also gives an additional Mental trait.
-The Abyss Creature is immune to Social challenges - but not Mental challenges.
-The Abyss Creature possesses at least one derangement as chosen by the ST as well as an obsession that resembles a sin from a path - as chosen by the ST. Each Abyssal Creature has a goal, which may not be the same as the one that summoned it. It can move independently at normal movement rate. Intense light will dispel the creature. The creature will exist for one hour or until destroyed.
-The summoner can repeat the ritual to reinforce the creature's presence. An additional hour long ritual against the same difficulty will allow the creature to exist until it is destroyed as long as the caster feeds it (15-Obtenebration levels) in blood per night.
-The summoner can attempt to absorb the manifestation into himself. This requires the summoner defeat the creature in combat. Once this is done he drinks its darkness into himself. He then gains the creature's attributes that are added to his own for the duration of the night. He also gains the creatures derangements and cannot spend Willpower to resist its effects.
-If the creature is able to reduce the summoner to torpor, it can invade his body and control it for the rest of the night. This is resolved with a Mental challenge. It can also return the following night and try again. If it can do this three nights in a row - it possesses the summoner until driven out.
-Driving out the beast involves another practitioner of Shadow Occultism to perform the ritual as described above.
-The summoner can summon any particular Abyssal Creature he has summoned in the past and it will have the same statistics. He must still perform the ritual however.
Descent into Darkness
-This ritual requires the successful use of Occult 5 influence in order to learn and is considered an advanced ritual - cost to learn is 6 XP.
-By performing this hour long ritual and expending on blood point and winning a Mental challenge vs. 9 traits the caster is able to physically enter the Abyss - the Obtenebration equivalent of Psychic Projection. The one big difference is the caster's physical body enters as well.
-The caster can move as if he has fleetness and peer into any real world environment in near or total darkness. He can step out of a shadowy spot and return to the real world. However, it does have its hazards.
-Every 10 minutes the caster spends in the Abyss there is the possibility that he encounters an Abyssal creature. If he wins or ties a simple test there is no encounter. If he does encounter an Abyssal Creature it will try to place him in torpor and possess his body as described in Summon Abyssal Creature above. The creature has the following stats: Physical Traits: 3, Health Levels: 3, Mental Traits: (Equal to the Caster's level's of Obtenebration +1), Potence, and a Derangement as determined by the ST. It also is obsessed with a particular sin, also as described above. Combat in the Abyss does damage to Willpower, just as in Astral Combat. However, if the silver cord is cut (all Willpower lost) the Abyss spits the character out into the nearest dark place in the material world.
As to your actual plot, I think it proves easier to deal with your potential storyline in an outline. I will provide questions which you can turn into plot hooks (I don’t know how many gamers you have, nor what clans they will be playing)
Child Embraced by a Malkavian.
· Who Embraced him? Why?
o Obviously he is a Malkavian – was it part of his dementia? Is he still around? Did he move on? Do the pc’s know him? Is he a major player in the City’s political realm? Maybe he performed the embrace while being Dominated… maybe someone else knew that a Malkavian embracing _this_ particular child would create this particular effect (see more below).
o Are there other children that have been embraced by this Malk sire, if this is a derangement?
o What gen is the Sire? The kid would have to be pretty powerful to pull this kind of stuff off… maybe the kid is half-fae, or the son of some powerful Mage?
· Is the Embracer Attribnu or Cam?
o If Cam, is he bloodhunted (most Princes view embracing children as a breach of the Masquerade)?
o If Sabbat, is he part of a local pack? Did the local head honcho give the ok, or is this a Malkie with a soft spot for kids?
· Is this part of a bigger game?
o Assume someone knew that the kid would manifest these powers – are they doing this to test what the kid can do, so that they can use him as a weapon somewhere else? Is this some distraction for something that is going to happen somewhere else? How did they know? Who are “they”?
o If this is totally random, why did it happen? Could it happen again? Is it something the sire passes on, or something about the kid?
Embrace creates unknown reaction in child, while in torpor-like state, he can manifest master level Dementation abilities, and causes a major problem.
· Who does this make trouble for?
o Are the mortals affected? Any of the other World of Darkness scions (Fae, Werewolves, Wraiths)?
o If this is not in the middle of the city (and therefore in everyone’s faces) how did anyone find out about it (how many people go wandering through that abandoned church 30 miles north of city limits)?
o Is the PC group going to be competing with other groups who may want to take the child for themselves, or end the threat themselves?
· Where is the kid when this starts happening? Does his dementation leave lasting effects on his surroundings?
o If this is in a city, and it is a Cam domain, who is going to keep the Masquerade going? How much Influence will have to be burned?
o Have mortals been killed by the dreams? If so, how are their deaths explained/dealt with?
· How long does this go on for? Who tries to stop it and fails before the Lasombra steps in? Are they successful in any way?
o There could have been a “first group” sent to deal with the issue before the PC’s go… and their hints, for the most part, come in following that group’s trail.
o Did the Lasombra have to separate the Sire from the Child? Is the Sire still a player (trying to protect his Childer perhaps)?
An agent of the Lasombra of fairly high power removes the Malkavian child from this plane by stuffing him into the Abyss.
· Is the Lasombra acting alone? Is he under orders from a Bishop? Why did he do what he did?
o Is he a rouge? If so, how did he find out about what is going on? Is he, perhaps, holding the childe in the hopes of drawing out the sire to Diable him? Why throw the kid in the Abyss? Why not kill him outright? Or torp him?
· What are the players going to have to do to find the Lasombra? Get him to cooperate with their demands?
o Perhaps there is something he wants. Perhaps he is using this situation as a test for his next big plan, and the PC’s will find themselves saved by the Lasombra’s intervention, only to owe him a boon that creates the next adventure…
o If the Lasombra is not looking for a deal, they may be in big trouble, unless the PC’s are damn powerful, they are going to have a heluva tough time with a Lasombra that strong.
o Do any of the members of the PC’s clan have ulterior motives or connections with the Lasombra? In a Cam situ, this would be the perfect time for one clan to weaken another, or expose some treachery or somesuch.
The players (for some reason) want to stop the kid’s manifestations – That becomes the goal of the final scene.
· If Cam: Who mobilizes the players? Do they have a choice? Are there any factional conflicting orders?
o Are they being called on boons? Is something dear of theirs hanging in the balance? Are one or more of the players related to/bonded with the childe/sire?
o If not called on boons, and the Prince is just mobilizing in force, do the Primogen carry additional agendas into the mission? Does this create conflict within the PC’s (ie the Tremere is supposed to get a sample of blood for study, but the Gangrel is supposed to reduce the body to ash)
o If this is a big breach of the Masquerade, or if other factions coming into play are going to be racing to stop/take the kid, how are the PC’s going to deal with the Prince’s law?
o Whose holdings is this taking place in? Are there any secondary agendas of the Prince’s along with the primary mission (ie retrieve the sire in torpor for sentencing, or destroy the Lasombra along with the child…)
· If Sabbatt, what is the motivation? Are they trying to subdue the kid, or take the kid to use him against the Cam? How does the Lasombra figure in to the local political scene? Anyone with that power is going to be pretty high up on the food chain within the Sabbatt.
o Does the Lasombra perhaps want the local Prince’s head as a toll into his little Abyss portal? Maybe the head of the local bishop he plans to usurp? Maybe both?
o Is there another local Lasombra that might be able to enter the Abyss to bypass the guardian? Is he equipped to deal with the Abyssal fiends?
o Are any of the gatekeeper’s friends or foes going to use this situation to try and take advantage of him? He cannot move far from the kid, so he is relatively tied down. Maybe he has been taken in by the dream, and is now under the control of the kid!
· In either case – are the players motivated by some clan or interpersonal sense of duty, or is there some greater personal gain they are looking to aquire out of this?
o The kid would make a mighty weapon, especially blood bonded.
o Diablerie is always fun – what effects would it have here?
o Rewards from the local undead society? Perhaps exclusive hunting rites or a herd….
o How is the Lasombra going to react to his party being crashed? If he was taken in by the dreams, then perhaps he owes a boon… if not, then the PC’s have a formidable foe for the future.