The material below is Open Game Content from a 3PP Source
Your critical hits with improvised weapons are much more damaging.
Prerequisites: Mahrog, base attack bonus +10.
Benefit: When attacking with an improvised weapon, your critical threat range is 19-20/x3. If you have the Club and Spear feat, for weapons affected by that feat with a lesser threat range than 19-20, the critical hit threat range increases to 19-20.
Normal: Your critical threat range for improvised weapons is 19-20/x2.