I'm pretty sure there was a "bug" in the Japanese version that accidentally let it happen but they updated it. So we're left out most likely.

How would you compare it to the original DS's Yoshi's Island sequel?

I'm about 99% sure that mystery island is a tribute to the Wind Waker. Looks EXACTLY like the beginning island.

You do know they technically gave Scyther one since Scizor has one, right?