Minecraft wiki entry for Before_1.18, associated text: The rare modified jungle edge variant generated only in strict conditions, and it was the rarest biome in the game. If a jungle biome bordered a swamp hills biome,[2] then the modified jungle edge spawned as part of a double-layered transition, with a thin normal jungle edge bordering the swamp hills, and the modified jungle edge bordering the jungle. As both jungles and swamp hills were already rare, and even more rarely did they generate bordering each other, the conditions for a modified jungle edge to generate were rarely met. When they actually did manage to generate, they were often just a few hundred blocks in length, but in some cases were less than 10 blocks, making them one of the smallest biomes as well. Modified jungle edges featured the same smooth transition and lowered tree density that regular jungle edges had, though with much more mountainous terrain and occasional overhangs. Ocelots, parrots, and pandas spawned in this biome, but jungle pyramids didn't generate here. Modified jungle edges covered only a few millionths (0.00027%) of the overworld by area.