The Nintendo Coin (also called "Rareware Coin" in some regions) is the final 101st collectible in DK64. Steps:
Collect All 100 Golden Bananas (25 per Kong across 8 worlds + Hideout Helm).
Beat King K. Rool in the final boxing match (Hideout Helm).
Enter the Bonus Barrel that appears after credits – it's labeled "Nintendo Coin Challenge."
Complete the Challenge: A timed race (2:30) through a custom course collecting 50 bananas. Use all 5 Kongs' abilities (Chimpy Charge, OrangStand, etc.).
Coin Awarded: Appears in Snide's HQ → Bonus Menu → Nintendo Coin. Also unlocks original Donkey Kong arcade game in the menu.