The mushroom boime seed is 4 that’s it. Just 4. Its a big mushroom biome with an end portal nearby in the sea. You can find the mushroom biome if you look to your right and swim across the sea. There is also a lot of open ravines and caves you may see at the bottom of the sea. It takes 30 seconds to type in the seed and load a new world. The co-ords for the mushroom biome are: X= 320 Y= -500
Minecraft Mushroom Biome Seed Video