Balloon Buster Punchcard is one of the simple challenges asking you to do one simple thing: shoot down a supply drop.
Fortnite Chapter 2 Season 3 introduced Punch Cards as a way to replace the Battle Medal system. The system should feel similar for players as they slowly chip away at dozens of objectives. When you reach one, you'll be rewarded with a large sum of experience points. And they all vary in difficulty with a few only taking a couple of matches while others will probably take a whole season to complete.
Balloon Buster Punch Card Fortnite: How to Complete
To complete the Ballon Buster Punch Card, shoot down a supply drop. That's it. Unlike other Punch Cards that cause you to work on something for a long period of time, this can be down in one single match, that is, if you find a Supply Drop. If you do so, you'll earn 14,000 experience points.
Good luck out there, and happy hunting. If you are looking to figure out the rest of the punchcards, look no further.