Silly Balloons are novelty blocks that can be purchased during a party from the Party Girl for 1 . When a single one is placed, it has a round appearance, just like Bubbles and Smoke Blocks. When balloons of the same color are placed together in groups, they connect to make a seemingly single larger balloon block. If placed adjacent to balloon blocks of other colors, they do not connect, and each will remain a single round balloon.
In a similar way to Pink Slime Blocks, landing on any balloon block causes the player to bounce.