In the vampire gamemode (which should be part of secret), a few players get spawned in as vampires (more players = more vampires). Vampires are immune to oxygen damage and maybe toxin damage if that's not too OP. Vampires have a few basic abilities when they're spawned in.
Feed
If you're grabbing someone aggressively, allows you to bite them, draining them of blood over time. This DOES work on catatonics, you DO get blood from them, it WORKS on monkeys too, it WORKS on dead people, ANYTHING THAT HAS BLOOD COUNTS FOR THIS. Also YES, blood bags count, YES glasses of blood count, DRINKING BLOOD FROM A CONTAINER COUNTS AS FEEDING.
Regenerate
Heals some brute damage. It's basically a weaker fleshmend.
Glare
Stuns a player immediately, but displays a message and the stun doesn't last very long.
Toggle night vision
Toggles your night vision.
Vampires gain power as they drain blood. You lose blood over time, and your powers take blood to use. You gain powers PERMANENTLY when you reach the blood threshold. Here are powers that you gain from reaching blood thresholds (please suggest more, these aren't enough).
Mesmerize
Takes a short time to complete, but stuns your victim for a good while.
Enthrall
Takes longer than mesmerize, but turns a player into your thrall. They are forced to obey you, and they have LIMITED antag status. They are ONLY allowed to do antag things if you tell them to.
Create vampire
Turns a thrall into a new vampire. They ARE allowed to harm you because this isn't cult. However, vampires are not allowed to harm each other 4noraisins.
They MUST have a real reason.
Vampires of course have some weaknesses. Holy water burns them like acid, bibles will always cause brain damage (never heal), and the holy weapon causes increased damage to them. They CAN drink the chaplain's blood, they CAN enter the chapel without bursting into flames, and they CAN walk into space without bursting into flames. They will go into a frenzy if they lose too much blood. In a frenzy, they become controlled by the AI and try to kill and feed on anything with blood they see.