The Nightmare Seed is one of the eight seeds that can be obtained and cultivated by the players from gardening, a feature introduced during the Ratboy's Nightmare Update.
- A possible 'rare' drop from the Spikers.
- A possible 'rare' drop from the Chewed.
- A possible reward from the Guttermouth Cells.
In appearance, the Nightmare Seed appears to be a pair of nightmare seeds with plump purplish-black roots. Other small blocks and fragments of the seed can be seen around the seed, as well as on the seed.
Players can use this to cultivate and grow a Nightmare Plant if they desire to do so. Other than that, players have the option to sell the Nightmare Seed to a selling vendor at a selling price of 8,000 gold.
- The Nightmare Seed is typically cultivated if the players need to unlock The Plant Room's door or to gain profit from the end-products (Fruit of Nightmares).