Because this is a modified ROM, running it requires specific emulation software.
: Alternative versions of characters with older movesets from KOF '97 or '98 Rebalanced Bosses : A playable version of kof 99 plus rom exclusive
In official versions, Krizalid is strictly a non-playable boss (unless playing specific home console ports like the Dreamcast or PlayStation versions, which still require beating the game). Because this is a modified ROM, running it
The cabinet’s clock finally moved. The ROM cartridge ejected itself, blank as if never written. Fighters walked away changed: some with lighter hearts, some with furtive gaps in memory that they felt but could not place. The arcade returned to ordinary hum — except when at night, when the neon flickered, a faint new melody played from the cabinet, and the memory of one man’s laugh warmed the lungs of a weary fighter. The ROM cartridge ejected itself, blank as if never written
So, what makes King of Fighters '99 Plus ROM so special? Here are some of the exclusive features that set it apart from the original game: