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Attacking With Shield
If you attack with a shield, treat it like an attack with an improvised weapon (see page 178). This deals the heavy shield bash damage or light shield bash damage (as appropriate to the shield’s type) listed on Table 6–5: Martial Melee Weapons on page 180.
If you want to reliably use your shield to attack, you need to buy and attach a shield boss or shield spikes to the shield. These work like other weapons, and can even be etched with runes (see page 370).
What does "reliably use your shield to attack" mean exactly? Does it mean that with a shield boss or spikes your shield strike is no longer considered an improvised weapon and you can now apply your proficiency?