Battle Arena Crown
From the Super Mario Wiki
Battle Arena Crowns, also known as Battle Crowns or Crowns, are collectible items in Donkey Kong 64 that resemble King K. Rool's crown. There are ten Battle Arena Crowns in total, one for each level (including the hub world, DK Isles). The Kongs can obtain a Battle Arena Crown by completing a timed Battle Arena Pad challenge, where they must avoid being defeated by enemies or knocked out of the arena.
At least one Battle Arena Crown is needed to unlock multiplayer mode. Four of them are required to open a door in Hideout Helm, allowing the Kongs to go down a pathway leading directly into K. Rool's throne room. The other six Battle Arena Crowns do not affect gameplay, but add to the player's 101% completion score.