In the standard arcade version, icons like Kyo Kusanagi and Iori Yagami are hidden and require specific cheat codes or high "Battle Ability" points to encounter. The Plus ROM typically makes these characters immediately selectable on the main screen.
Unlike previous 3v3 entries, KOF '99 introduced 4v4 teams where the fourth member acts as a Striker —a support character called in with a button press to disrupt or extend combos. Kof 99 Plus Rom
Many unofficial "Plus" editions include "Combo" hacks that allow for easier special move canceling or infinite gauges, catering to a more casual, high-intensity playstyle often seen in "bootleg" arcade cabinets. The King of Fighters '99 Mechanics In the standard arcade version, icons like Kyo