A Blue Nethershroom is a poisonous blue fungus simillar to a Warped Fungus found in the Other Dimensions, more exactly the Warped Forest.
Natural Generation
Blue Nethershrooms are found abundantly in the Warped Forest, where, if an entity walks on them, they explode into blue poison clouds.
In most nether missions and ancient hunts, they can be thrown by the Fungus Thrower and the Zombified Fungus Thrower.
In the camp, they can be found in the Mystery Merchant's stand and the Piglin Merchant's cave.