I was playing a single-player hardcore world when a Drowned spawned on the steps of my house, which is in mushroom fields. I'm aware that other biomes can overlap mushroom fields, such as ocean biomes and lush caves, but it spawned in the middle of the island, out in the open. The island is large and doesn't have any ruins nearby. It was night and raining, which could have contributed to its spawn. I also checked the F3 menu to just to confirm the biome, and it was the mushroom fields. Here's the seed and exact coordinates where it spawned just in case anyone needs them X:7821 Y:81 Z:8963 Seed:2350749701994258865