Nightshade is one of the many plant resources you can find while exploring Hades 2. It's a valuable ingredient that you can expect to use in many of your enchantments, which unlock various upgrades and unique spells to aid you on your journey against Chronos.
Hades 2 How to Get Nightshade Seeds and N-Shade Farm Location
Unlike the other resources, Nightshade can be a bit trickier to find. It only spawns in a specific region of Hades 2, and you’ll need to be patient with it. Like all plants, Nightshade takes a while to grow, and you can expect to need a lot of it for the various spells Hecate teaches you.
You can find Nightshade by exploring the first region in Hades 2, Erebus. You won't find it from enemies or as a room reward. Instead, you'll need to dig it up using the Silver Spade, which you'll need to unlock at the start of a game before starting a run, under the Harvesting Tools page.
More advanced crafting recipes will be unlocked for you, including the Silver Spade, after you unlock the Crescent Pick and can start collecting Silver. You can craft the Silver Spade for 10 Silver. Once you’ve done this, make sure to grab the Silver Space before you start running and interact with any dig sites you come across while exploring Erebus. These contain a handful of Nightshade seeds, which you can then take back to camp.