Actually, you can fake it with runtime expressions on the spriteScaleXPP and spriteTwistPP attributes. It IS a fake, but depending on what you're going for, it can work. Try something like this. Creation expressions: particleShape1.spriteScaleXPP = rand(-1,1); particleShape1.spriteScaleYPP = rand(-1,1); particleShape1.spriteTwistPP = rand(-180,180); Runtime expressions: if (particleShape1.spriteScaleXPP > 1) { particleShape1.spriteScaleXPP = -1; } if (particleShape1.spriteTwistPP > 180) { particleShape1.spriteTwistPP = -180; } particleShape1.spriteScaleXPP += 0.01; particleShape1.spriteTwistPP += 2; Attached is a sample file to see what I mean. I'm very excited to help Mike after all the times he's helped me. I hope it works.