Your modified spells are impossible to analyze and Greatly confuse other spellcasters.
Benefit: When you cast a tricky spell or any spell that has been modified by a metamagic feat, your opponents are unable to determine which spell you are casting, even with a successful Spellcraft check. Any auras that these spells leave are also impossible to analyze: they register as magical auras of indeterminate type and strength. If another caster attempts to identify such a spell as you cast it, they are denied their Dexterity bonus to Armor Class for one round.
Undefeatable: The Collected Feats Sourcebook, Copyright 2009 – 2010, Louis Porter Jr. Design, Inc. Undefeated, Copyright 2011, Louis Porter Jr. Design, Inc.