So I don't know if there is a true forme of Giga Bowser but I have fought a Bowser that is slightly tougher than a normal Bowser. I don't know if that's Giga Bowser or not, but I've also seen videos of people fighting a mewtwo and a ganondorf teamed up with him. I have never played SSBM that far to fight Giga Bowser with those 2.

Giga bowser in ssbm can be fought two ways:
1. on event match #51
2. beat adventure mode on hard or very hard with 3 lives in under a certian amount of time

Giga Bowser is a boss in Melee if you do the above mentioned. However, certain mods (mainly GameShark or Action Replay cheats) allow you to play as Giga Bowser in standard Melee battles. I assume that is what you saw.

It looks pretty similar to the Brawl Giga Bowser, but, iirc, it is smaller...

The other Bowser is not Giga Bowser, it is just a 1.5 X bigger than normal Bowser

Mr. GayManWatch wrote:The other Bowser is not Giga Bowser, it is just a 1.5 X bigger than normal Bowser

You see, that's what I'm thinking. I challenged it in normal mode, and I got this Bowser that was too easy and I was like "Gigafail D:"

TheBlueYoshi wrote:So I don't know if there is a true forme of Giga Bowser but I have fought a Bowser that is slightly tougher than a normal Bowser. I don't know if that's Giga Bowser or not, but I've also seen videos of people fighting a mewtwo and a ganondorf teamed up with him. I have never played SSBM that far to fight Giga Bowser with those 2.

That is event 51.You have to beat events up to 50 to get it (iirc). It's pretty hard imo. However, you'll feel SO good when you beat it.