Here is the full list of all 12 The King of Fighters '98 Ultimate Match achievements worth 200 gamerscore.
Achieve 100 wins in Xbox LIVE fight.
Achieve 50 wins in Xbox LIVE fight.
Achieve 10 straight wins in Xbox LIVE fight.
Achieve 10 wins in Xbox LIVE fight.
Achieve 5 straight wins in Xbox LIVE fight.
Finish the game ( can't lose one round, can't continue) ( Arcade/Single Play Only ).
Finish the game (can continue) ( Arcade/Single Play Only ).
Highest point exceeds 300 thousand ( Arcade/Single Play Only ).
Perform an assist attack ( Arcade Play Only ).
Pass level perfectly in one round (without injury) ( Arcade/Single Play Only ).
Iori(Ura) or Leona(Ura) appear as CPU ( Arcade/Single Play Only ).
Achieve straight win ( Arcade Play Only ).