Counterweights

A Counterweight is an accessory sold by the Traveling Merchant and the Skeleton Merchant, for 5 gold, but only the green, blue, red, yellow, black, and purple variations. It shoots out a second damaging item after hitting an enemy with a yoyo. It seems to be sold at a specific time, but it is unknown what time that it will be sold at (around 12PM apparently). Additionally, it is used to create a Yoyo Bag. Six versions are known: red, green, blue, purple, black, and yellow. Although multiple counterweights can be equipped, only one counterweight can be used at any time. The Counterweights all appear to be dice. The blue and red varieties appear to be tetrahedral dice, the purple and green ones cubic dice, and the black and yellow ones dodecahedron dice.

"Blow on it".