I was reading about Young Master Xehanort on the KH wiki, and it says that when Mickey shows up near the end of DDD and casts Stopza, YMX is able to move, summon a Keyblade, and fight Riku because he's being temporarily possessed by Master Xehanort. I have absolutely no problem with this theory, as it explains why his eyes glow yellow for a moment right before the fight starts, despite the fact that we've never seen a human character do that before, as well as his declaration of "Begone!", which I've always thought seemed a bit OOC. I'm just wondering, how do we KNOW that MX was actually possessing YMX? Is it stated in some other media that I don't know about?

If I remember correctly, Nomura stated it in an interview after Dream Drop Distance came out in Japan. Too tired to find it though, but I'm sure it's in the archives here

MX does have multiple forms. Doesn't that explain it?

YMX is a time traveller so he can't be affected by this kind of time magic. He's not "possessed", he has just received this power by MX.

— Did King Mickey’s time magic not work properly on Young Xehanort because Young Xehanort has the power to control time?

Nomura: Not Young Xehanort’s but rather Master Xehanort’s power. King Mickey was surprised at the time, seeing his Keyblade and noticing he harboured the power of Master Xehanort. That Keyblade was designed as the one Master Xehanort used in KHBBS combined with an hourglass, you see.

It's not a theory .It's confirmed fact .

 

 

 

— Did King Mickey’s time magic not work properly on Young Xehanort because Young Xehanort has the power to control time?

Nomura: Not Young Xehanort’s but rather Master Xehanort’s power. King Mickey was surprised at the time, seeing his Keyblade and noticing he harboured the power of Master Xehanort. That Keyblade was designed as the one Master Xehanort used in KHBBS combined with an hourglass, you see.

 

  Plus this quote from Nomura as well :

 

— When King Mickey stopped time, Young Xehanort began to move. Since he can control time, was he breaking the King’s spell?

Nomura: Young Xehanort wasn’t using his own power at that time. The King’s magic was broken because Master Xehanort was assimilating with Young Xehanort. Only “the mark of heresy” was added by Organization XIII.

— It was when the figures started appearing in the thrones.

Nomura: Indeed. Time was stopped just as Master Xehanort was materializing. So he moved his consciousness to Young Xehanort’s body. Reacting to this, King Mickey exclaimed, “That’s impossible!” Young Xehanort was holding a Keyblade that he originally wasn’t able to handle thanks to Master Xehanort’s power. Though the keychain on it is different, the Keyblade he takes out is Master Xehanort’s.

It's not a theory .It's confirmed fact .

 

 

  Plus this quote from Nomura as well :

 

— When King Mickey stopped time, Young Xehanort began to move. Since he can control time, was he breaking the King’s spell?

Nomura: Young Xehanort wasn’t using his own power at that time. The King’s magic was broken because Master Xehanort was assimilating with Young Xehanort. Only “the mark of heresy” was added by Organization XIII.

— It was when the figures started appearing in the thrones.

Nomura: Indeed. Time was stopped just as Master Xehanort was materializing. So he moved his consciousness to Young Xehanort’s body. Reacting to this, King Mickey exclaimed, “That’s impossible!” Young Xehanort was holding a Keyblade that he originally wasn’t able to handle thanks to Master Xehanort’s power. Though the keychain on it is different, the Keyblade he takes out is Master Xehanort’s.

 

Great! Thanks, Flaming Lea!

This also explains what Mickey's thinking in the English dub when he says, "Oh no, are you-?" after YMX summons his Keyblade.

Great! Thanks, Flaming Lea!

This also explains what Mickey's thinking in the English dub when he says, "Oh no, are you-?" after YMX summons his Keyblade.

 

Yup and you are welcome .

I was reading about Young Master Xehanort on the KH wiki, and it says that when Mickey shows up near the end of DDD and casts Stopza, YMX is able to move, summon a Keyblade, and fight Riku because he's being temporarily possessed by Master Xehanort. I have absolutely no problem with this theory, as it explains why his eyes glow yellow for a moment right before the fight starts, despite the fact that we've never seen a human character do that before, as well as his declaration of "Begone!", which I've always thought seemed a bit OOC. I'm just wondering, how do we KNOW that MX was actually possessing YMX? Is it stated in some other media that I don't know about?

He's got the "Time Power". Even Stopza doesn't affect him.

It was more like MX arrived at the exact time Mickey coasted the spell so MX was able to influence YX and gain control of him.

I thought it had something to do with time travel