The BK2 file contains the ROM I used, hopefully that's okay...? (It's no longer available to download anywhere.)
It's not very exciting, but holy shit, the lag was horrible. Way more than it had any right to be. The game has is about delivering mail along a route of seven areas. Pressing A will fire a bullet, and holding B will start an aiming cursor a la Yoshi's Island on Hasty mode. The issue is that it aims to the NORTHeast when you first start holding B, so getting up close to the mailboxes is the best way to save time.
The game has three criteria it checks for: mail delivered, enemies defeated and lives lost. If the majority of mail is delivered, the majority of enemies are defeated, and no lives were lost, you get a "Great!" rank and get to take on the final boss, which I took a hit on to skip most of the death sequence. The lives are shown in the upper-left as three... white and pink thingies? Pills? Nitrous rockets? I don't know, but in any case, you only ever get three.