Theory of this deck:
1. Defenders are cheaper mana costs compred to non-defenders due to the limitations that come with them, such as not attacking & having 0 power. This deck's commander lets us both attack & do substantial damage with 0/X creatures. That means we will get more value for the same mana cost as our opponents.
2. The commander ability also provides great card advantage since we'll be playing lots of cards with Defender.
3. Most Defender creatures have low or 0 power, so the deck can use removal and board wipe spells that target high-power values.
4. Use enchantments to +make our permanents either hexproof, shroud, or indestructible as much as possible to keep them on the board longer.
5. Good walls & defenders are usually cheaper to buy.
6. Being attacked by walls is hilarious and needs to have a deck built around it.