Every beast will level up after every double wave. This increases the attributes of it and makes the beast much stronger. "Melee" beasts will only attack your protectbase on contact. "Ranged" beasts attacks your towers until everything is demolished on it´s way to your protectbase. Beasts with type "Both" will have a non direct ranged attack and move straight to your protectbase to deal contact damage. Contact damage will always kill the beast directly without the earnings on death, because it´s an attack.