Game mechanics: Venom-like Symbiote

[Aaedimus]

I'd like my adventurers to encounter and have to deal with some type of slime or pudding than ends up having venom-like symbiotic properties (at first... over time, it slowly consumes its host).

They will have to fight them, but may end up in simbiosis too. I'd also like the symbiotes to all share a collective conciousness.

How would you build game mechanics for something like this?

[HappyDaze]

I'm not sure, but in my campaign, I've used the following for something similar:

Shadow Demon + Young Black Dragon = Shadow Dragon

The Shadow Demon is "within" the Shadow Dragon and when the Shadow Dragon is defeated, the Shadow Demon is unharmed and appears within 5' to fight (or, more likely flee).

[Sorinth]

The easiest way to handle it would be to treat the symbiote as a sentient magical item.

[iTreeby]

The easiest way to handle it would be to treat the symbiote as a sentient magical item.

In 3.5 there was a magic item type called a psychoactive skin, a cursed or sentient version of such could work. Definitely make the host interesting in their own right too though, they might survive!

[jjordan]

My take. And I ended up making these a sort of magic item, while possessed by/hosting one of these the character cannot attune to any magic items and loses any attunements they had.
https://forums.giantitp.com/showthread.php?611202-Shadow-Variant&highlight=shadow

[Damon_Tor]

I'd like my adventurers to encounter and have to deal with some type of slime or pudding than ends up having venom-like symbiotic properties (at first... over time, it slowly consumes its host).

They will have to fight them, but may end up in simbiosis too. I'd also like the symbiotes to all share a collective conciousness.

How would you build game mechanics for something like this?

Morgrave Miscellany (Kieth Baker's Eberron Supplement) includes a new Pact Boon which is exactly this, a symbiotic creature that can be a blessing or, if you lose control of it, a curse.

It's... it's not great. It has serious wording issues, there's some confusing stuff, and the balance is questionable at best. But it might be a good place to start looking.

[DrKerosene]

For NPCs, I’d probably just do what’s explained by TheAngryGm in his “Son Of The Bossfight” article series (which is basically to use 2+ creatures, but say it’s only one creature for narrative purpose, like a Knight on a Warhorse and saying it’s a Centaur).
Having two creatures taking Reactions and movements at different times would probably seem like a typical Symbiote creating pseudopods to do things.



Alternatively, I think something with the Possession ability would probably be a decent base creature. Also the Dybbuk and Intellect Devourer seem like they could work if tweaked to be less lethal/one creature in control.



Off-hand, I think the Warlock Invocations Mask Of Many Faces and Fiendish Vigor would be a good base-line for classic Symbiote abilities (or just glamor armor and some kind of HP regen). Maybe it could count as a set of Ogre Strength Gauntlets (or a belt of giant strength). (Modified by invocation) Eldritch Blasts or Thorn Whip could be the “webbing” for swinging, or maybe a Rope Of Entanglement.



The collective consciousness could just be a permanent Rary’s Telepathic Bond spell like effect, or maybe just the Detect Thoughts spell being an at-will ability that is always on and concentration free.

[Damon_Tor]

I'd like my adventurers to encounter and have to deal with some type of slime or pudding than ends up having venom-like symbiotic properties (at first... over time, it slowly consumes its host).

They will have to fight them, but may end up in simbiosis too. I'd also like the symbiotes to all share a collective conciousness.

How would you build game mechanics for something like this?

Just going to spitball here:


You're infected with a symbiote. Treat this like a disease or curse.

Whenever your character cannot take actions (usually because its under the effect of some condition, or even unconscious/dying) the symbiote takes over and takes your actions for you.

At the start of its lifecycle, this is generally helpful: you weren't using that action anyway, and the actions taken by the symbiote on your behalf are generally helpful, the symbiote wants to keep itself, and thus you, safe. It spends your actions dodging or disengaging and spends your movement moving away from danger. All it wants in return is for you to eat double rations at every meal: it absorbs half for itself.

In the second stage of its life cycle (maybe a week later) it becomes more aggressive about when it can take control: it takes your body out for a joy ride whenever you sleep. Notably this doesn't interfere with your ability to get a long rest, you sleep right through this "sleepwalking" and all the thing seems to have you do is look food. Your friends might be annoyed when "you" rummage through their bags at night and devour all their rations, but this isn't super harmful, and you discover you can keep it busy by hiding food around the campsite for it to search for.

The third stage (another week or so) is where it becomes potentially harmful. At this point any dead creature within 5 feet of you triggers an immediate wisdom save from you, and if you fail it, the symbiote takes control and starts eating the corpse. Every turn you can repeat the save to take back control, and on a successful save you can take your turn as normal. Also at one this phase, when it takes over for you when you're stunned or whatever, it is more likely to charge the enemy and make unarmed attacks than to dodge and disengage.

On the fourth stage (another week passes), it can take control of your body once per hour, forcing you to make a wisdom save, and on a fail it uses your body to attack the nearest creature with an unarmed strike and try to eat it. At this stage, if it goes more than 24 hours without eating a freshly slain creature of small size or larger, it starts eating you instead, reducing your maximum hitpoints by 1d10 every hour until it is fed. The actions it makes you take during this phase are increasingly reckless: it WANTS you to die now, so it can enter the final phase of its life cycle. So falling asleep during this phase will often result in your flinging yourself out of windows and such.

If you reach 0 hitpoints during the fourth stage of the creature's life cycle, you die and it controls your corpse. It stops trying to feed: at this point it becomes driven to leave "eggs" in places where creatures are likely to stumble upon then. After about a week of depositing its 3d4 eggs, your corpse finally gives out and the creature dies having fulfilled its biological imperative.