Matt's main strength is his ability to deal large amounts of damage from his main weapon, which spreads and can wipe out many enemies at once. To get the most value out of this, you must:

1. Make sure you are only firing when you have enough charge to maintain spread
2. Are far enough away that the spread reaches multiple enemies

Additionally, make sure that you are using your diamonds effectively by shooting off as much of your spread as possible before picking up the diamond.

Matt's best sub is the Holy Swords. This is because it stores a lot of damage in charge, and that same charge can be expelled rather quickly.