Use a variable to hold the value for where you want the bar to be, then another variable for where the bar actually is, and use curvevalue to bring it close to the target. This should work:
rem Kenshin's Health Bar
KenshinHp#=curvevalue(KenshipHptarget#,KenshinHptarget#,3.0)
Box 78,23,KenshinHp#+78,59
Do
Rem Testing the Health Bar
If keystate(2)=1
KenshinHptarget#=KenshinHptarget#+1.0
endif
If keystate(3)=1
KenshinHptarget#=KenshinHptarget#-1.0
endif
rem Conditions for victory and loss
if KenshinHp#<0 then goto Game_Over
if ShoMP#<0 then ShoMP#=0
if KenshinHptarget# > KenshinMaxHp#
KenshinHptarget#=KenshinMaxHp#
endif
if KenshinMPtarget# > KenshinMaxMP#
KenshinMPtarget#=KenshinMaxMP#
endif
Xander Moser - Bolt Software - Firewall