Yeah, I concur with McA. Create a new class for each type of enemy.

package Enemy {
  use Moo::Role;
  has wounds => (is => 'ro');
  ...;
}

# Look how tiny these classes are.
# Creating lots of classes doesn't have to be painful.
package Rat { use Moo; with 'Enemy' }
package Cat { use Moo; with 'Enemy' }
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Also, please don't use Moos for anything serious. I'm an officially listed as a co-author of it, so I'm entitled to say that. ;-)

Use Moo, or Moose, or Moops. Here's my above example using Moops, showing how it eliminates a lot of boiler-plate code.

use Moops;

role Enemy {
  has wounds => (is => 'ro', isa => Int);
}

class Rat with Enemy;
class Cat with Enemy;
[download]

Let's extend that a little with some attack types:

use Moops;

class Attack {
  has name   => (is => 'ro', isa => Str);
  has damage => (is => 'ro', isa => Int);
  method light ($class: ) {
    state $me = $class->new( name => 'light attack', damage => 1 );
    return $me;
  }
  method heavy ($class: ) {
    state $me = $class->new( name => 'heavy attack', damage => 3 );
    return $me;
  }
}

role Enemy {
  requires "get_attack";
  has wounds => (is => 'ro');
  method is_weak () { $self->wounds > 5 }
}

class Rat with Enemy {
  method get_attack (Object $target) {
    return Attack->light;
  }
}

class Cat with Enemy {
  has lives => (is => 'rw', isa => Int, default => 9);
  method get_attack (Object $target) {
    return Attack->heavy;
  }
  around is_weak () {
    return false if $self->lives > 2;
    return $self->$next(@_);
  }
}

class Monkey with Enemy {
  method get_attack (Object $target) {
    $target->is_weak || $self->is_weak ? Attack->light : Attack->heavy
+;
  }
}

class Ninja with Enemy {
  method get_attack (Object $target) {
    return Attack->new(name => 'ninja attack', damage => int rand(5));
  }
}

class Priest with Enemy {
  method get_attack (Object $target) {
    $target->is_sinful ? Attack->heavy : Attack->light;
  }
}
[download]

That kind of thing.