You need to move the onComplete, onCompleteParams outside the css:{} object like below,
TweenMax.to(bg, 1, {
css: {
scaleX: 1.5,
scaleY: 1.5,
transformOrigin: "center center"
},
onComplete: reverse,
onCompleteParams: [bg],
delay: 0.2,
ease: Power3.easeInOut
});
function reverse(el) {
alert("Sdasd");
TweenMaxto(el, 0.6, {
css: {
scaleX: 1.0,
scaleY: 1.0,
transformOrigin: "center center",
autoAlpha: 1,
},
ease: Power2.easeOut
});
}
Check the fiddle
Hope it helps.