Old swampland_mutated downfall no longer matches swampland downfall
In 1.21.60.27 preview, the downfall value of the swampland biome was changed to 0.9 to match Java Edition. However, the swampland_mutated biome, which is used in worlds version-locked to 1.17 or prior, is still using the incorrect 0.5 value.
From the data/definitions/biomes/swampland.biome.json file in the app package:
From the data/definitions/biomes/swampland_mutated.biome.json file in the app package:
Expected Result
Swampland and mutated swampland biomes have identical downfall values of 0.9.
Observed Result
Mutated swampland still has an outdated downfall value of 0.5.
Linked Issues
Created Issue:
Old swampland_mutated downfall no longer matches swampland downfall
In 1.21.60.27 preview, the downfall value of the swampland biome was changed to 0.9 to match Java Edition. However, the swampland_mutated biome, which is used in worlds version-locked to 1.17 or prior, is still using the incorrect 0.5 value.
From the data/definitions/biomes/swampland.biome.json file in the app package:
From the data/definitions/biomes/swampland_mutated.biome.json file in the app package:
Expected Result
Swampland and mutated swampland biomes have identical downfall values of 0.9.
Observed Result
Mutated swampland still has an outdated downfall value of 0.5.
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I can confirm that the swampland downfall has been changed to 0.9 to match Java Edition. However, the swampland_mutated downfall has not been fixed. This is reported as MCPE-189877.





Thank you for your report!
However, this issue has been closed as Working as Intended.
The requested change is on a legacy biome which is as such version locked.
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I am not sure Works As Intended is the correct resolution for this bug. This is because, even in version-locked worlds, the swampland downfall has changed from 0.5 to 0.9 in 1.21.60.27.
1.21.60.27 causes a mismatch between swamp sub-biome properties in version-locked worlds. The swampland_mutated downfall should be updated specifically to fix version-locked worlds, because otherwise, 1.21.60 will introduce a weird inconsistency.