Find the Weak Spot, Greater (3.5e Feat)
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Greater Find the Weak Spot [General]
You are able to find the weak spot on non-living entity allowing you to critically damage it.
Benefit: You increase your critical hit chance to 75% (D100 roll 25 or higher to hit) against creatures that would normally be immune (treat immunity as 100%). This feat also affect sneak attack and similar abilities.
Normal: You cannot achieve critical hits against undead, construct, elemental and certain other creatures with immunity to critical hits.