Lord Godwin
The Lord of Darkness
Johto Starters (or even Unova) would be great with those huge forms. Since Charizard most likely has a Gigantomaxxed form it would be more than proper for Venusaur and Blastoise to have ones.I also think that at some point in the game the player is given a Kanto starter just like in XY.
Also a Gigantomaxxed Butterfree might be funny.