OnHeartbeat - check to see if the character is in combat then do the other checks. However, using heartbeats can be processor intensive depending upon what you are trying to do.
OnCombatRoundEnd - checks if a combat round just ended.
OnAttacked - checks if a character was just attacked.
If you look at the BIC files for the pre-generated PCs, you'll see they all have a built in "default" script - no actual script in the game, but if you create one it will be recognized and accessed - which is used to handle ALL PC event calls if it exists.