In ‘Night Terrors’ the sinister dolls have the ability to change others into versions of themselves. This ability is particularly scary for an alien or monster to possess. Not only will you effectively ‘die’ you will become the enemy.
The ‘Aliens and Creatures’ book does include Infection as a major good alien trait. This is perfect for simulating this form of attack, as well as being suited for zombies or vampires.
When the player characters are facing opponents with the ability they need to think tactically. If the infection is spread by touch they can’t afford to get within close range, making combat difficult.
They will also need to think about what they are going to do if one of them become infected. Do they retain their personality and memories? Could that be used against them if one of the player characters is infected?
In zombie films the discussion often turns to whether a person would want to live if they’ve become infected. Things can take a very dark tone if player characters have to start killing each other to avoid a fate worse than death.
In an adventure with infectious enemies the player characters can quickly find the tide of battle turning against them, as more and more people become infected. From encountering a single monster they can soon find themselves outnumbered.
A plentiful number of NPCs can act as a buffer for the player characters. This allows the enemy to demonstrate their infectious qualities while still giving the player characters time before they are directly affected.
This can be especially effective if the NPCs were particularly nice or had useful qualities. It is even more horrible when the NPC is a regular cast member, whether it be an ally, friend or family member.
Player characters will need to think about how they will contain the infection. The enemy needs to be isolated and those infected quarantined. There is also the horrible consequence of the enemy getting out into a large community where the player characters will have no chance to contain its spread.
This can serve to push the player characters into a terrible decision. They can choose to protect themselves but if they do the enemy will escape and spread. If they choose to fight then they risk infection themselves.
The nature of the infection can greatly affect the adventure. Does it affect everyone equally or are only certain people vulnerable? If it is race specific the player characters may very well be immune (especially if the adventure is taking place on an alien planet).
The infection might target specific groups, for example a computer virus that only infect cyborgs or robots. It might only trigger in specific circumstances like at night, underwater or in zero gravity.
By making an infection only after certain groups those people become pariahs. Even if they aren’t affected or the infection has long since been wiped out other groups will shun them, out of fear.
This allows for adventures that focus on issues of prejudice. Does this minority group band together or take on a nomadic existence? Do they hide their identities? Where they specifically targeted?
To avoid making the enemy seem harmless to those immune to their infection people should still be in physical danger. It is small comfort to know you’re immune to the zombies infectious bite when the undead are eating your internal organs.
You will also want to know if the infection can be cured. If it can’t then the enemy can be shown no mercy, destroyed to stop their disease spreading. This does make things grim for player characters who are infected, effectively taking them out of play.
If there is a way to cure people things become more complicated. The infected can’t simply be engaged in combat if there is a chance that they might be hurt or killed. They are victims who can be saved, even if they are attacking the player characters.
The race to find a cure, before the enemy and the infected defeat them, can be an exciting quest for the player characters. They must discover if it is possible, then once they have found a cure they must find away to reproduce it and spread it to all the infected.
This is the best route to take if you wish to have player characters infected but still allow for them to be saved. It also makes the stakes more personal, as their allies now how even more reason to find a cure.
Player characters might think the easiest thing to do when facing an infection is to escape in their TARDIS. This could have the unfortunate consequence of spreading it to other parts of space and time.
It could be revealed that someone on board was infected, that the symptoms sometime aren’t displayed immediately. One of the infected could have stowed away or the TARDIS itself could act as a carrier.
Rather than escaping the infection the player characters will only succeeded at spreading it even further. Before they can travel in the TARDIS again they will need to find a way to stop the infection for good.
Player characters could also have to deal with the consequence of their actions while they were infected. Once cured do they remember what they did? Do they feel guilt? If they don’t remember do they wonder about these gaps?
This may change their relationship to other player characters, especially if they did or said something hurtful while infected. Can others accept that it wasn’t really them or can they never forget what they are capable of doing?