Mad Mole Holes
The fight is similar to Whac-a-Mole, and it takes place in a single-screen cave, with three holes on the ground through which Hard Hat periodically pops up. While no Buddy Barrel is broken on-screen, both Donkey Kong and Diddy Kong are available from the start, regardless of their previous status.
Hard Hat is invulnerable while wearing his miner helmet, although touching him does not injure the Kongs (despite the fact that they flash briefly as if they had taken a hit). He does not turn around after emerging from the hole, even if the Kong in play jumps over him.
After a moment, Hard Hat throws his helmet in the direction he is facing, which injures the Kongs if they touch it. This is similar to how King K. Rool attacks by throwing his crown. This provides the Kongs an opportunity to jump on or even walk over Hard Hat. There's a "hit" sound if a Kong actually jump on him, but if they walk over him there is no additional sound, although it still counts as a hit. If the Kongs do not hit Hard Hat on time, he dives back down into his current hole, and re-emerges with a helmet back on his head.
After every hit, Hard Hat speed increases and the window where he is vulnerable before retreating shortens. Hard Hat is defeated after taking eight hits, and three Banana Bunches fall from the ceiling as a victory prize (just like when other boss fights are won), and the Kongs move on to Big Ape City.