I don't know if this is a glitched rom or anti piracy.

I was playing Kingdom Hearts: 358/2 days and a strange thing happened.

Spoiler

In the fight against the Clay Armor the game suddenly started lagging as soon as the bottom screen played a flashback of some sort of Sora fighting in the coliseum.

The problem is the game would stop for a few seconds and even though you could still hear the sounds of the action you just cant see the action going. I am using Desmune .94 x86.

Upgrade to 0.9.5.
Or use No$gba instead.

That happened on my NOGBA too. Sora showing up is a normal part of the game, but for some reason the game gets really slow when it happens. As son as that ends the game goes back to normal.

It happens to me too, though if you have a stronger PC the lag will be less visible.
The Emulator isn't strong enough to provide that kind of screen I guess.You have to bear with it I'm afraid.