The other day I was thinking about something to add to D&D and I came up with a type of Mushroom that grows native in dark, damp caves that are fed by a pocket of adamantine, or perhaps mithril. You can work it into your campaign however you want, but it helps if there’s either a magical source feeding it, or an unusual metal. I like the idea of Dryads cultivating them for their own dietary needs, and protecting the grove, and as a result the adamantine or mithril, from miners. (That could be a story hook in and of itself.)
The mushrooms offer a faint glow in the caves, providing as much light as a firefly. If picked, they lose their glow after about an hour. If ingested, there are some pretty interesting side effects. Something not often dealt with in D&D games is addiction; there are some supplemental rules that offer various ways to handle it, but it’s not part of the core game. (And why should it be, necessarily? Addiction is dark, gritty, and horrifying in real life; we want to have fun, not be depressed.) But if you handle addiction purely from a stats point of view, (and late the players determine what else happens to their character) that can be fun.
If ingested, these mushrooms give a +2 to strength and a -2 to Wisdom and Charisma. The effects last 8 hours, + 2 hours for each additional mushroom eaten while under the influence. A constitution save will prevent addiction to the mushrooms. I have a formula worked out for determining the save DC, (to make increased use == increased chance for addiction) that I will share at the end of this.
If a player becomes addicted to the mushrooms, there are no changes until they go into withdraw. Withdraw begins 24 hours after their last mushroom. They suffer withdraw for half the amount of time they ate the mushrooms. So if they ate for 10 days, then they suffer withdraw for 5 days. Withdraw symptoms are: -2 to Strength, Dexterity, and Constitution. Withdraw can be temporarily stopped by eating a mushroom, but when the player enters withdraw again, they start over from the beginning. (That is to say, if they started with 5 days of withdraw, and on the 3rd day they ate a mushroom, and then entered withdraw 24 hours later, they would be in withdraw for 5 days again.) If the player feeds their addiction for more than one day, it adds to the number of days that they are addicted for purposes of determining withdraw time. (So, if they entered withdraw and had 5 days of withdraw ahead of them, but on the 4th day began eating mushrooms again, and did so for another 10 days before running out, they would have 10 days of withdraw ahead of them instead of the 5 they started with.)
You can determine the save DC using this formula – roll every time they eat a mushroom:
DC 15 + (2 for each mushroom they’ve eaten in a day) + (2 for each consecutive day they’ve eaten mushrooms)
So if the player ate 4 Drydak Mushrooms on the first day to get 14 hours of the bonus, their first save would be 17, 19, 21, and then 23. If they ate 4 the next day, it would start at 19, (2 for the first day they’ve eaten the mushroom, and 2 for the first mushroom), and then 21, 23, 25. If they become addicted, they do not need to roll saves anymore; they are addicted, and the addiction lasts until they have completed withdraw.
As an optional rule, you can add a +5 to the DC if they’ve been addicted before, so then the formula might look like this:
DC 15 + (2 for each mushroom they’ve eaten in a day) + (2 for each consecutive day they’ve eaten mushrooms) + (5 if they’ve been addicted to Drydak Mushrooms before.)
Hope you can use this in your campaign; if you do, tell me about it!