Coal is used to spawn creepers and build certain advanced structures like the kaboomery. It's fairly rare, but you can find coal deposits in most biomes
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— Coal journal entry
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Gather coal from the chosen area. Coal unlocks advanced structures and can be used to spawn creepers. Coal deposits can be found in the meadow and badlands.
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— Gather coal resourcing melody
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Enables gather allays to collect coal. Each additional improvement allows you to carry: +150 coal. Coal unlocks advanced structures and can be used to spawn creepers. The first upgrade grants +25 coal and enables village chests located in meadow or allay chests in any biome to contain coal.