Giga Bowser is a Boss canidate for SSB4. He is very big and mean. He should return as an individual character from the original Bowser. After Boss defeat he becomes another of Bowser's Final Smashes again. To meet him, play Adventure Mode with any character under normal or higher without continuing. Here's some quotes:
"SUFFER MY WRATH!"
"YOU WILL DIE! MUHAHAHA!"
"YOU DARE BRING LIGHT TO MY LAIR!? YOU MUST DIE!"
"ARRGH, YOU MUST DIE!"