Here's a breakdown of why this matters:
* Attack Damage: When your opponent's monster attacks your monster with 0 DEF, the full attack damage goes directly to your Life Points. You don't get to subtract the DEF from the attack, as you would with a monster with a positive DEF value.
* Battle Phase: Monsters with 0 DEF are often used strategically in the Battle Phase. They can be used to absorb attacks for your other, stronger monsters, or used as bait to lure out your opponent's more powerful cards.
* Special Abilities: Some monsters with 0 DEF might have special abilities that make up for their lack of defense, such as the ability to destroy other monsters or to inflict damage to your opponent directly.
Examples:
* "Sangan": A popular card with 0 DEF that allows you to special summon other monsters from your deck.
* "Cyber Dragon": A powerful card with 0 DEF that can summon other Cyber Dragon monsters from your deck.
* "Morphtronic Cruncher": A monster that gains DEF based on the number of other monsters on the field. It can start at 0 DEF but gain a lot of defense quickly!
Important Note: Even though a monster with 0 DEF is vulnerable, it's not always a bad thing! It can be a strategic advantage in many cases, especially if you can use its special abilities to your advantage.