Opacity Behavior
This behavior changes a particle's opacity over the course of its lifetime using a curve.
OpacityCurve: A curve which controls the opacity of the particle over its lifetime. The current fraction of the particle's lifespan is used for the lookup along the X axis. A value of 1 means fully opaque, 0 means fully transparent.
This behavior provides more control over particle transparency than the simpler Fade Out Behavior, allowing for effects like particles that fade in, stay visible, and then fade out.