Something I have been experimenting with in my game is having creatures inflict system strain as a replacement for old-school energy drain. For example, a vampire’s touch inflicts 1d6 system strain and gives you a penalty (e.g., Drained +1). If that puts your system strain over its max, you die and become* a vampire three days later. That makes them scary without the screw you of losing levels.I have a whole limited healing house rule somewhere on my computer (sorry, I'm a bit drunk right now, not gonna search for it) inspired/lifted from Worlds Without Number after @kenada told me about the mechanic. One of the worst parts about d20 healing is that there is basically no way to slow down a party for multiple days, which is what I feel I always want to do; I rarely have things you need to rush to do, and when I do I want those moments to feel particularly risky and frenetic. So I made up some rules based around the limited healing idea from that system. I haven't really tried it yet, but I want to in the future.
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I also gave the transformation a chance of failing. You have to make a Physical saving throw then a Mental saving throw (or Fortitude and Will, in PF2 parlance) both at a −2 to the roll. The first is to survive the transformation, which is not guaranteed. The second is to avoid becoming mindless. In-setting, undead are afflicted with a curse of intelligence, which requires them to obtain something from the living lest they lose their minds and become mindless monstrosities. Vampires need blood, ghouls need flesh, etc. It varies from creature to creature how often and to what extent they must feed.
60 mL of blood is good for about three days, but 5 L (or exsanguinating someone) is good for about a year. You can’t get it incrementally. It has to be in one feeding. The time between required feedings is based on the quantity of your largest feeding. The only way to increase your current interval is to feed enough that it’s “worth” more. I have a formula for calculating arbitrary feedings based around the two numbers above. The idea is to make it needing a feed a potential source of conflict. You can’t just get someone to trickle blood to you regularly, and it has to be from intelligent creatures (so no animals).
The way succumbing to the curse works is your senses start to dull about a week before you need to start making saving throws. When the time comes you must feed, and you haven’t, then you start making a Mental saving throw every day when you wake. While you are making these saving throws, all Mental saving throws incur a penalty equal to the number of days you’re in your stupor. In practice, this isn’t a big penalty (because undead are immune to most effects that require a Mental saving throw), but it means you will eventually succumb if you don’t feed.
60 mL of blood is good for about three days, but 5 L (or exsanguinating someone) is good for about a year. You can’t get it incrementally. It has to be in one feeding. The time between required feedings is based on the quantity of your largest feeding. The only way to increase your current interval is to feed enough that it’s “worth” more. I have a formula for calculating arbitrary feedings based around the two numbers above. The idea is to make it needing a feed a potential source of conflict. You can’t just get someone to trickle blood to you regularly, and it has to be from intelligent creatures (so no animals).
The way succumbing to the curse works is your senses start to dull about a week before you need to start making saving throws. When the time comes you must feed, and you haven’t, then you start making a Mental saving throw every day when you wake. While you are making these saving throws, all Mental saving throws incur a penalty equal to the number of days you’re in your stupor. In practice, this isn’t a big penalty (because undead are immune to most effects that require a Mental saving throw), but it means you will eventually succumb if you don’t feed.