The Mark, a contagion mechanic for your vampires

 I can't remember what came first: Vampire Hunting Weekly, or the idea for a defensive mechanism that turned vampire hunters into, well, vampires themselves. If you're not familiar with VHW, well, it's a small OSR/NSR game I've been working on, and while I originally planned to release it on Halloween, the odds of that happening are not in my favor. I did manage to finish most of its mechanics, though, and you can read my favorite one below!

THE MARK

Vampires are unquestionably the planet's most adaptable apex predators, as evidenced by the diversity of their Strains. It is no surprise, then, that they developed an insidious defensive mechanism when humanity started fighting back.

Those that survive a confrontation with a vampire, whether they emerge victorious or not, run the risk of being Marked by their quarry. Said Marks manifest as the most undesirable aspects of vampirism, and the stronger a vampire is, the more likely they are to inflict a Mark. Likewise, the more Marks a hunter has, the closer they are to becoming what they hate. 

The odds of being Marked are always X-in-6, with X being determined by the enemy's Hit Dice — after killing a 3HD Feral, you'd have a 3-in-6 chance of receiving a new Mark. On the other hand, if you survived a violent encounter with a 6HD Broodmother, you would automatically receive a Mark.

When a hunter receives their First Mark, they roll once on the blights table and reroll an Ability Score of their choice. If the new result is higher than their current score, keep it. If it's lower, ignore it.

After receiving their Second Mark, a hunter rolls twice on the blights table and rerolls their Hit Protection with a d20. If the result is higher than their current maximum HP, they get to keep it.

By the time a hunter receives the third and Final Mark, they're dangerously close to permanently losing their humanity. They roll three times on the blights table, doubling their maximum Hit Protection, rolling a d6 for each Ability Score and adding the results to their respective scores. The next time they're Marked, there will be no turning back.

BLOODLINGS

After receiving a fourth active Mark, a hunter ceases to be a playable character and turns into a Bloodling — a wretched, subservient creature somewhere between a mortal being and an immortal predator.

Bloodlings are inherently drawn to True Vampires, for they are the only ones who can complete their transformation into a creature of the night. When claimed by a vampire, Bloodlings become their loyal servants until released, killed or turned.

COMPATIBILITY

This mechanic should be compatible with most OSR/NSR games, as VHunt is built upon the foundations laid by Into the Odd and Cairn. It will add an element of horror to any campaign it's used on, however, so make sure you and your players are on board with that before hand!