Boss villains are usually invulnerable all over their body, with the exception of one or a few weak points which you can often attack For Massive Damage. Therefore, if you see a shiny or glowing target anywhere on the boss villain's body, chances are that's where you need to attack. Common targets are the head, eyes (particularly if it's a cyclops), hands (if the monster is giant), tail, groin (if it's male), the inside of the mouth, any built-in weapons, or a soft underbelly. Machines often have a gratuitous red Power Crystal or Heart Drive that practically screams "Hit me!".