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The Mafia has the ability to cast a protection spell on one of their members, shielding them from all attacks. If Darza correctly guesses the target, he can eliminate several players. Shruk has complete immunity to magic. Also, it's likely that the town's mages won't attack on the first night but will spend their mana on healing or blocking, and then they'll have enough mana for one attack, followed by a recharge. Perhaps the Dragons should have their UD (Undead Defense) removed, as there's an excessive number of fire-based attacks, and Oromis should probably have his melee attack removed.

Added 54 minutes later
I've removed UD from all the town's Dragons and removed the physical attacks from Eragon and Oromis. Now, Eragon can only attack with magic, which is limited by mana, or with a combined attack with Saphira, but then he can't use his own Night Defense (ND) that night.