The blue nethershroom is a poisonous blue fungus similar 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 the camp, they can be found in the Mystery Merchant's stall and the Piglin Merchant's cave.