The King of Fighters '98 Ultimate Match is a remake of The King of Fighters '98 which includes all characters that were present up to The King of Fighters '97 (making it the only dream match game with the most complete roster of characters based to date within the KOF series as a whole).
Additionally, new alternate versions of characters were added (such as EX Blue Mary and EX Yamazaki). Meanwhile, other alternate versions of characters (barring the Orochi New Faces team and Omega Rugal) gain brand new portraits from their original versions (both on the order select and on the character select/HP-bar mugshot).
