When you jump to that state, you would then check if the grenade is close enough to do damage and how much. Then subtract that from your players health.
The player is throwing the grenades, how do I inflict damage on the beast? My other thought is to
put the playmaker stuff I know into fpskit, it has the shooting bad guys thing going well, vehicles, etc., but
no dialogue, inventory, puzzles. Either way is a lot of work.