itch.io

The part which applies the move is the part (starting at line 671) which begins:

//Apply to all target(s) individually
for(var c = 0; c < array_length(a_targ); c++){

Currently it doesn't do anything special to detect targets not existing, it checks if the number of hits is 0 and the number of misses is also 0 to conclude that there was no target after the fact. (Done immediately after this loop)

So what I'd do is insert a check before this loop, which checks if the original target remains, otherwise gets a random one based on the move (using the function enemies use to pick random targets):

found_targets = 0;
for(var c = 0; c < array_length(a_targ); c++){
     var trg = a_targ[c];
     if(battle_is_alive(trg)){
         found_targets++
     } 
}
if(found_targets == 0){
     a_targ = battle_get_random_targets(a_user, a_comm); 
}