Character mistake: When the first case's true murderer is KO'd by Phoenix's amazing attorney skills, he is carried away from the courtroom. The Judge then asks to the prosecutor, "Mr Payne, your client?" He should have obviously asked, "Mr Payne, your witness?" And that's exactly what he asks in the Trilogy remake, that fixes this mistake.
Character mistake: During the tutorial, Phoenix needs to be reminded a few things. The judge asks him the victim's name, and Mia Fey next to him tells him where to look to get that information. Her line though is flubbed, since instead of "the victim's name" she says "Look, the defendant's name is in the Court Record." This mistake was spotted and fixed in the "Ace Attorney Trilogy" remake.