You want to spawn a random mob in one certain cave? If so it could be triggered threw your Envir/MapQuest.txt. You could go.
[@main]
#IF
!HOUR 19
#ACT
MonGenP "10,337,153,150" BadAssTaurus 1
10=the map
337=x coordinate
153=y coordinate
150=area close to x,y coordinates
and badasstaurus 1= 1 mob