Minecraft wiki entry for Experimental_Gameplay, associated text: "Wild Update"
Enables work-in-progress features from The Wild Update.
"Vanilla Experiments"
Enables work-in-progress features that may be included in future versions.
"Holiday Creator Features"
Enables add-ons features added on the holiday update and some further updates that include the creation of custom blocks and items, Molang enhancements and the run_command method.
"Custom biomes"
Enables custom biomes by using add-ons.
"Additional Modding Capabilities"‌[until BE 1.18.30]
Enables the old scripting features.
This experiment is due to be removed from the game by March 2022. Worlds using these features will continue to load but gameplay will be impacted.[3]
"Upcoming Creator Features"
Used for Volume Driven Fog and entity properties and permutations.
"Gametest Framework"
Enables GameTest Framework automation tool feature.
"Molang Features"
Enables experimental Molang features.