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When you are bitten by a zombie, you have to make two checks against Fort DC 10+HD of the zombie. If one fails, you turn into a zombie in 1d4 days, if both fail, you turn into a zombie in 1d2 days. In 1d4 hours your base land speed drops by 33%. In 2d8 hours after that, you take a -3 penalty on reflex saves.

This homebrew is meant for an ECL 1 DnD 3.5 zombie survival campaign. I want to know how much I should (or even if I should) change zombie CR by.

EDIT: I will use the zombie plague but with the following modifications: The infected automatically die in 3d4 days if they don't stave off the disease. The DC is 10+HD

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    \$\begingroup\$ Welcome to rpg.se! What is the story effect you're hoping to achieve with this mechanic? \$\endgroup\$ – BESW Apr 26 '16 at 0:48
  • \$\begingroup\$ I want to make zombies dangerous to the party and explain the mass prevalence of zombies throughout the campaign world. I also want motivation for them to attempt to find the cure and the cause of the plague. \$\endgroup\$ – Burgeoning DM Apr 26 '16 at 11:17
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This should be an enormous increase in CR.

Basically, you're giving every attack the zombie makes a "save twice or die" effect. Unless there's some easy way to cure this infection outside of combat, your entire party will be dead within a week.

There's a reason Left 4 Dead and some other zombie games/media often imply or outright state that the main characters are, for whatever reason, immune to (or asymptomatic carriers of) the zombie disease: not being immune makes survival mostly a matter of being very, very lucky.

Let's say a character gets attacked by 4 zombies. Each zombie has only a 25% chance of hitting the character, and the character has only a 25% chance of failing their save. Further, let's say that each time all the surviving zombies have attacked, the character kills one (so the character is attacked 10 times: 4+3+2+1). If they only have to save once to be safe, the character only has a 52% chance of not being infected at the end of the fight; if they have to save twice, it's a 31% chance. And that's a single fight.

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  • \$\begingroup\$ Would the increase be as massive if it was one save? \$\endgroup\$ – Burgeoning DM Apr 26 '16 at 0:36
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    \$\begingroup\$ @BurgeoningDM They can't be lucky forever. Characters will get bitten. Characters who get bitten will eventually fail a save. Period. You either need some way to cure the disease or you need to expect that the average character will only survive for a couple sessions. \$\endgroup\$ – Oblivious Sage Apr 26 '16 at 0:39
  • \$\begingroup\$ @BurgeoningDM Being able to cure it seems like a good compromise. You could have them go in the night to the woods to search for some herb every time they get infected. \$\endgroup\$ – Roflo Apr 26 '16 at 15:30
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Try instead the disease zombie plague

To challenge the frame, I suggest you roll instead with published material. The description of the 4th-level Sor/Wiz spell animate infectious zombie [necro] (City of Stormreach 144) includes this disease:

Zombie Plague: The disease carried by an infectious zombie has an incubation period of 24 hours. After that time, a victim who failed its Fortitude save loses 1d6 points of Constitution. An additional save must be attempted every day thereafter until the victim either succeeds, negating the plague, or dies, rising as an infectious zombie.

An injury from a zombie's natural weapon spreads the disease; it has a Fort save DC of 16.

The game codifies diseases and provides ways to deal with diseases that are both mundane (like the Heal skill's treat disease and many feats1) and magical (like the spell remove disease). The save DC is high enough that commoners frequently fail and unprepared low-level PC worry but not so high that it's impossible to deal with. (Your sample effect, for example, has otherwise CR 6 creatures with a special ability that has a save DC of 30.)

About this special ability

A special ability that kills days after the creature's encountered shouldn't increase a creature's CR significantly unless the effect is very difficult to delay or remove. Such an effect can still kill folks, but treasure gained from such encounters should permit them to get help to end the condition before it kills them. However, the shorter the interval, the more deadly the effect, and the more you should look at increasing a creature's CR because of it.

For example, the onset time of the mummy's the mummy rot is 1 minute. If unprepared and infected, there's not time enough to return to town for a remove curse followed by remove diseaseand dying from it means turning to dust and being blown away, so no raise dead and maybe no resurrection either. That's scary.2 But rarely are stories told of adventurers bitten by dire rats who then die after contracting filth fever. With its onset time of 1d3 days, filth fever is just annoying, and dire rats aren't significantly more dangerous because of it.3

Without any way to remove your example's effect, after a few days, an adventurer who fails the save will be a zombie. That makes the only "cure" succumbing to the effect, becoming a zombie, having someone kill you, then having someone cast on you raise dead. That's probably worth a +1 to CR because the effect will kill a few PCs but, afterward, the party, knowing what they're up against, pays strict attention to proper adjudication of encounter distances and Dumpster-dives for ranged weapons that deal slashing damage, and the effect will only come up rarely.


1 In addition to the many feats that grant bonuses to saving throws against disease, there're feats like Deformity (Parasite) (Elder Evils 13) and, obviously, Disease Immunity (Heroes of Horror 121-2). There are also feats that are more interesting in a zombie plague-ridden setting but less common otherwise, like Invoke the Cup and Talisman (Dungeon #104 107), Planar Touchstone (Empyrea Mere (Planar Handbook 155)) (Magic of Incarnum 207), and Vathrin Stigmata (Dragon #319 61).
2 I kid you not. The description of mummy rot says that a creature that dies from it "shrivels away into sand and dust that blow away into nothing at the first wind" (MM 191). Fanciful? Yes. Terrifying? O, yes.
3 Well, to adventurers, anyway. To low-level commoners, dire rats remain a scourge.

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  • \$\begingroup\$ Really glad this got pointed out. While not an answer to the actual question, this will probably be a great help to the asker. \$\endgroup\$ – Joninean Apr 28 '16 at 12:58
  • \$\begingroup\$ +1 BUT (as a side note) according to asker's comments the world will be filled with zombies, therefore while not explicitly stated, the real world effect would be a drastic increase in the price of & even lack of availability of healers kits (& related herbs etc). Depending on PC level this concern could be of varying concern. \$\endgroup\$ – Ben-Jamin May 21 '16 at 0:25
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Using these "CR 1" zombies against a party of an appropriate level is a nearly guaranteed TPK. The Oblivious Sage has explained that, and I could elaborate a little on that:
A CR 1 zombie would be a Troglodyte zombie. One of the "normal" Troglodyte zombies should be a relatively easy encounter for a level 2 party. This zombie has 4 HD, which means the save DC would be 14. Presuming a good Fort save and a 14 Con, the odds that the party will make that save is ~65%, for they'll have to roll 7 or higher in order to make the save. ~42% to make that save twice. And these would be the odds per attack. I'm not even going to mention what happens if a character has a poor save.
Now, presuming the fighter got hit by an attack of this zombie, and failed a save, then that fighter has literally become a timebomb, and a TPK waiting to happen. The fighter will turn into a zombie with 2 HD and we can start all over.

Using these adjusted zombies against parties of higher levels (presuming you're sticking to the CR 1 zombies) is flat-out boring. It's balanced poorly for your average D&D adventure: it's basically a TPK if it gets a single attack off. One of the few ways to effectively avoid this, is by one-shotting it, but then the party is too high level for this sort of encounter.

And if you're not sticking to the CR 1 zombies... The save DC they'll have to make would be immense and simply unfair. For instance, a Bugbear Zombie (CR 2) would already have 6 HD, which means a save DC of 16. And it only gets worse.

This homebrew can hardly be given an appropriate CR. It's good for its original purpose, namely a zombie survival game, but in your average D&D campaign, these zombies shouldn't be used.

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If it is only the bite of the zombie, that is infectious, then not every combat need be that deadly. Maybe the zombies usually try to grab or swing at the characters and can only try a bite after they have overwhelmed of incapacitated someone. In that case the CR would not increase that much. But if it's really every scratch, that dooms the character, then see the previous answers :-)

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    \$\begingroup\$ Deliberately using weak tactics doesn't change the CR of the monster. \$\endgroup\$ – Miniman Apr 26 '16 at 12:04
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    \$\begingroup\$ @Miniman: Why would that be deliberately weak? Maybe their bite, like a human's, doesn't deal damage, and maybe it is even disadvantageous in combat (provokes an AoO, can only be used on a pinned opponent, etc.). The sample zombie in the SRD doesn't have a bite attack, after all. \$\endgroup\$ – Charles Apr 26 '16 at 14:23
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As Oblivious Sage says, these monsters will kill your players if they get in melee combat. Do not calculate a CR or hand out exp according to the CR formula, as these are a plot device, not a monster. Your level 1 characters have as much chance against these as they do against the Legendary Tarrasque.

Tarrasque:

CR: 20.

Speed: Less than your players.

Ranged attacks: None.

Flying: None.

Turns in melee to destroy the party: 1.

Infectious Zombie:

CR: ?.

Speed: Less than your players.

Ranged attacks: None.

Flying: None.

Turns in melee to destroy the party: A couple.

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  • \$\begingroup\$ Yup, that sounds like a great comparison. So... maybe CR +18 or +19? ;) \$\endgroup\$ – Roflo Apr 26 '16 at 15:25
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As others already pointed out, such a thing would basically have a very high CR due to its "save or die" mechanic...
However
I can see many ways to make it fairly balanced again. First of all, the DC is just too high. Consider something like 5+HD, or maybe take the classic "15+characteristic" approach.

That being said, for example, can this be considered a disease? Maybe a difficult to cure one? An example would be the classic monster from SRD, Mummy. The monster has challenge rating 5 and it inflicts this disease with every attack. It is kind of hard to cure, but it can be cured. In the case of a zombie campaign, if many characters get infected, it would not be so easy for the cleric of the party to heal everyone... or himself.

Another approach could be making the attack more difficult to do, something like the Vargouille kiss. I would word it like

A zombie that has successfully pinned an opponent during grapple can attempt to bite him to infect. If the attack succeeds, the opponent has to make two checks ...

or maybe

*A zombie that has successfully pinned an opponent during grapple has automatically bitten his neck. The opponent has to make two checks... *

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  • \$\begingroup\$ ... and the infectious bite is a full round action? \$\endgroup\$ – Roflo Apr 26 '16 at 15:27
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The attack is deadly, as other posters have said, but it's postponed and melee only. How it effects the CR depends on how easy it is to cure. If it is easy for characters to counter during the incubation period then it should only have a mild effect. Also, the slowing effect of the disease suggests that you are also going to slow your zombies down. If their move is only 20' (can't run) then the party can defeat them with clever tactics.

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It shouldn't. Adding an instant death attack like this to a CR 1 monster leaves you with something that the CR system simply wasn't meant to cover.

To a low level party, these monsters are potentially deadly, since they can kill in a single attack. Even at level 4, a wounded character still has a <50% chance of making the double save. To a party with access to Cure Disease, they are trivial.

The problem is that you are trying to use D&D 3.5 for something it is not meant to do. D&D is about heroes fighting things, where permanent wounds almost never happen. For a zombie survival campaign, look into using a different system such as All Flesh Must Be Eaten.

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