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Acks are small, red enemies who appear in Donkey Kong Country Returns and Donkey Kong Country Returns 3D. They are a stronger and faster variant of Toothberries and also have sharp teeth. Acks are also related to AckStacks and Cageberries.
Acks only appear in the level Itty Bitty Biters. Like Toothberries, Acks jump around and follow the Kongs upon noticing them. They can jump higher than Toothberries, and Donkey Kong can defeat them by jumping on them twice (unlike Toothberries, who are instantly defeated from a single jump). Acks can be instantly defeated from a Kong Roll. If Donkey Kong and Diddy Kong get in contact with an Ack, they lose a heart.