I create enemy from top of stage with a time intervals of 0.5 sec. and also create enemy after 30 sec from left out side of stage with 0.2 sec intervals. First one fall dow by shape.gravity. Second one also do same but they have extra force aginst (new Vec2(0, 500)) and add extra (new Vec2(0, -300)). It's work fine on computer but slow run at mobile when second type enemy create.