Assuming player.react_before.poisoned (to use a neutral syntax since syntax is the topic) sounds like a way of setting (and getting?) an event handler, how about something like the following:

sub name {
   my ($self, $name) = @_;
   $self->{name} = $name if @_ >= 2;
   return $self->{name};
}


sub react_before {
   my ($self, $event, $handler) = @_;

   if (@_ >= 2) {
      $self->{event_handlers}{$event}{before} = $handler;
   }

   return $self->{event_handlers}{$event}{before};
}


sub poisoned {
   my ($self, $poisoned) = @_;

   if (@_ >= 2) {
      if ($poisoned != $self->{poisoned}) {
         my $handler= $self->{event_handlers}{poisoned}{before};
         $poisoned = $handler->($self, 'poisoned', $val) if $handler;
      }

      if ($val != $self->{poisoned}) {
         $self->{poisoned} = $poisoned;

         my $handler = $self->{event_handlers}{poisoned}{after};
         $handler->($self, 'poisoned', $poisoned) if $handler;
      }
   }

   return $self->{poisoned};
}


$char->react_before(poisoned => \&handler);

$char->poisoned(1);

print(
   $char->name,
   ' is ',
   $char->poisoned ? 'posioned' : 'not poisoned',
   ".\n"
);
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