To do this, create a `?fort_character` which extends the internal `game_action_causer` and `game_action_instigator` classes. Then, you can use `FC.Damage()` with `damage_args` like this:
FC.Damage(damage_args{Instigator:=Causer, Source:=Causer, Amount:=1.8*(1.0+TimeOnTarget)})