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AckStacks are yellow Acks that appear in the game Donkey Kong Country Returns and Donkey Kong Country Returns 3D. They are sub-species of Toothberries. They are found in groups of five and appear one atop the other in a tower. If Donkey Kong gets too close to them, they will lean back, then fall with their mouths open, attempting to defeat him. However, if Donkey Kong jumps back, dodging the monsters, they will land separate from each other, stuck on the ground. When single, Acks are vulnerable to jump attacks. Unlike normal Acks, they will only take one hit each. On a side note, the Kong Roll has no effect against the AckStack, but the Kongs won't get injured for attempting this maneuver.