Githyanki Battlecaster( Monster Manual IV, p. 202)
A creature with this feat ignores arcane spell failure chances when wearing light armor.
Ability to cast 2nd-level Arcane spells, Base attack Bonus +3, Githyanki,
The creature ignores arcane spellfailiure from any kind of light armor it wears.If it wears medium or heavy armor, or caries a shield, it has the normal arcane spell failiure chance.
A Fighter or Wizard may select this feat as a bonus feat for those classes