This made me laugh.

How would this card Shifting Homura work if it copied Shortsighted Madoka? Would Shifting Homura be exiled too or would Shifting Homura have already entered the battlefield and therefore ETB effects of the copied card wouldn't trigger?

Buh.

I have no idea.

I'm pretty sure Shifting Homura would also be exiled because if you copy a creature with a ETB ability, the copier gets the ability, right? If I remember correctly, weren't people copying Acidic Slime with Phyrexian Metamorph and using the slime's ETB ability?

You do indeed get the ETB triggers of the thing you're copying when you use any Clone that "ETBs as a copy of" whatever. (Clone, Phyrexian Metamorph, Shifting Homura, and many more.) So yup, Shifting Homura doesn't work too well on this one.

Turn 1: Torpor Orb

Turn 2: this x2

Assuming a Lotus Petal or Chancellor of the Tangle, sure.

Yeah, it's great with Torpor Orb, but not as dominating as Eater of Days, Leveler and so on.

I decided I wanted something to make Shifting Homura more immediately viable without having to wait for your opponent to cast something good and then exile that creature. Is making this a cast trigger too weird? Should I give the card another ability? Maybe trample?