example.php

class Creature extends Model {

   protected $with = [
       'entity'
   ];

    public function entity(){
        return $this->morphTo();
    }

    public function __get($key)
    {
        return $this->getAttribute($key) ?: $this->entity->getAttribute($key);
    }

}

abstract class CreatureType extends Model {

    protected $with = [
        'creature';
    ];

    public function creature(){
        return $this->morphOne(Creature::class, 'entity');
    }

    public function __get($key)
    {
        return $this->getAttribute($key) ?: $this->creature->getAttribute($key);
    }

}

class Human extends CreatureType {}

class Lion extends CreatureType {}