Warp Weapon - Truespeech

Pre-requisite roll: Roll a d20 and add your INT modifier. A 12 or higher is a success.

You analyze and name a weapon to make it more effective at finding the weakness in defense, or less effective at hitting the target. On a roll of 18 or 19, the wielder of the weapon scores a critical hit as if the wielder rolled a natural 20 (if, with additions, the weapon does not hit the target on an 18 or 19 due to AC, the hit misses)

Alternatively, you can lessen the power of the weapon. The wielder can resist with a strength saving throw of 18 or higher. On a fail, the weapon cannot perform a critical hit and the weapon is -2 for the duration. 

If the wielder saves, the weapon cannot be afflicted for a day.