Mithral Weapons

Quote from Wysperra >>

So Adamantine Armor has special properties, Adamantine Weapons have special properties.

Mithral Armor has special properties, but Mithral Weapons do not.

Any suggestions as to what I could include in my game? Nothing game breaking just a little something to make them better than run of the mill weapons.

Thanks!

 5.5e adamantine weapons are already insanely broken, especially since they're only classified as "uncommon." When combined with barbarian's Brutal Critical and one of the Slasher/Crusher/Piercer feats, you do massive, debilitating damage with every strike. Just give mithral weapons an equally broken ability that's the opposite of the armor version like adamantine is; something like ignoring all cover, invisibility, and illusions like a Mirror Image spell or a Cloak of Displacement, or even just the ability to always hit a target.