Speed defines the speed of rotation of the clusters. A negative value reverses the direction of rotation.
Decay controls falloff for the Rotation value. 0% means no falloff, 100% means the Rotation value falls to 0 as the clusters reach the edge of the blast range.
Use Variation to vary the rotation for each cluster.
By default, each cluster rotates about its center of gravity. Here, you can make clusters rotate around the X axis, Y axis or Z axis only of the world system. This is useful for special effects, logo animation and so on.
Use Variation to tumble the clusters.