Tales of the Twilight Coast
When a player, NPC, or monster rolls a natural “1” on an attack it will be an automatic miss regardless of adjustments to the attack roll per the PHB. In addition, the DM will determine a special effect appropriate to the specific situation such as a dropped weapon, falling prone, or loosing the next round of attacks. Severity of said effect is at the discretion of the DM.
Additionally, in the rare case that a player, NPC, or monster rolls two “1’s” on an attack roll when attacking with advantage or disadvantage the DM will determine a severe consequence appropriate to the specific situation up to and including a broken weapon, injuring an ally, or injuring self.