Tatanga should be a playable character. He or E. Gadd would've been way better than stupid R.O.B. But the thought of...
*Luigi peers into a barred window of a dank dungeon*
Daisy: WA-HOOOOOO! Luigi! You've come to rescue me!
At that point, I'd be like "Ah, nope, I've gotta go. Got a dentist appointment." Anyway, I don't think Aliens wil be the antagonist of a Mario game for a while, so soon after the Shroobs.