Rare Biomes Seeds

Since 1.18 the game picks every Overworld biome from a set of noise maps: temperature, humidity, continentalness, erosion and weirdness, plus depth for the caves. A common biome covers a wide spread of those values. A rare one needs a narrow mix of several of them at the same spot.

Ice spikes need a frozen climate, low humidity and high weirdness together. Frozen rivers usually separate them from the snowy plains around them, and they never border a forest. Snow blocks cover the ground instead of grass, and the spikes themselves are packed ice: short ones about 15 blocks tall and thin ones that can pass 50. In Java, strays take four out of five skeleton spawns under the open sky and shoot arrows of Slowness, and rabbits and polar bears are the only animals that spawn there.

A bamboo jungle needs a warm, very humid climate with positive weirdness, and there is almost always a lush cave under it. It is the place for pandas. In Java their spawn weight is 80 there against 1 in an ordinary jungle, though they never spawn on the podzol the bamboo grows from. Cherry groves sit on mountain slopes and plateaus in medium climates. Pigs, sheep and rabbits are the only animals that spawn in one, about one cherry tree in twenty carries a bee nest, and no village can start there, while pillager outposts can.

Mangrove swamps take the place of ordinary swamps in hot climates, beside deserts, savannas and jungles, and they never border the ocean directly. The floor is mud, slimes come out at night between Y=50 and Y=70, and in Java bogged spawn there as well. Frogs spawned in a mangrove swamp are the warm variant. A frog takes its variant from the biome it spawns or grows up in, so tadpoles raised in a snowy biome become cold frogs and tadpoles raised in an ordinary swamp become temperate ones. When a frog eats a small magma cube it leaves a froglight in its own color: pearlescent from warm frogs, verdant from cold ones and ochre from temperate ones.

The deep dark sits under mountains and other low erosion ground, mostly inside the deepslate layer. No mob spawns there through the normal cycle. Wardens come from sculk shriekers instead, and setting shriekers off four times brings one up out of the ground. Ancient cities generate only in this biome, with their floor at Y=-51, and their chests hold things you can't find anywhere else, such as Swift Sneak books and echo shards.

Adventuring Time in Java 26.2 asks for 55 biomes. Only the Overworld counts, and the list has all four cave biomes (lush caves, dripstone caves, the deep dark and sulfur caves) as well as pale gardens and mushroom fields. Mushroom fields sit far out in deep ocean and the deep dark lies deep underground, so plan a separate trip for each of those two.