From the Super Mario Wiki
Krockhead Barrels are usually found hovering in the air. If Diddy or Dixie Kong touch the barrel, it will summon several KrocHeads, which the Kongs can use to cross large gaps. The KrocHeads summoned by a Krockhead Barrel will only be surfaced above the water temporarily, meaning that the Kongs will need to hop on them quickly, before they vanish back in the water.
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