Where does the second Luigi from Galaxy come in?Stealing thunder from Blof,
Baby Mario was born after Mario, they're two different people. E. Gadd calls it a time machine but really it's just another world with similar inhabitants, that's why all the "present day" people didn't remember the Shroob Invasion.
Thunder from Lefty,
The Mario Brothers are triplets. Mario, Identical Luigi, and Non-identical Luigi.
The grave we see in SM64 is Identical Luigi.. but he lives! For he is playable in Super Smash Bros. under the name Mario.