I would still use else if. It makes clearer for the reader what is going on on a glance. That said it doesn't matter for how the code runs with return.

Is it preferred to chain a bunch of 'ifs' rather than the typical 'else ifs'? Or is it just whatever you want to do it fine?

FArrekkusu, I knew the first item would take its place but I didn't know it would in turn not get squared/cubed. Thanks for the reply.

Because the first item inside the array will take its place, and it will not get squared/cubed.

Why does leaving off the optional initial value paramater make or break this kata?

Read how reduce works

You're reducing the numbers incorrectly. You didn't even understand the task.

I didn't say they had the same input, I said they equate to the exact same value.

There're no 2 fixed test cases with identical input and different expected result. What are you talking about?