Viridian Imitator (3.5e Alternate Class Feature)
From D&D Wiki
Nature has made you more in tune with the abilities of others rather than spells.
Replaces: Spell casting ability, Spell Slots
Benefit: Add: "Perfect Imitating (Su): A ranger that sees an enemy use an ability that she can learn (See: Notes), she may make a check modified by her intelligence modifier and imitator level to determine if she learns it. The DC is less if the ranger is actually hit with the technique. When a using a technique use her Intelligence instead of Wisdom or Charisma and her imitator level instead of Hit Dice or Character Level. Imitator level equals one half ranger level. DC=10+(Enemy's HD)×2 or: DC=10+(Enemy's HD) iff the ranger was hit with what they are trying to imitate." to third level class features.