Just something I need to clarify before my players take this feat. If an opponent has IUD and a flanking PC has Outflank, does IUD negate the effects of this feat? Does it negate the effects of any flanking feat like Seize the Moment?
Improved Uncanny Dodge negates flanking. Therefore you can't get any other bonuses that depend on flanking.
Also you'll get more help if this is in the rules forum as this is a rules question.
Ok, I'll check there as well. Thanks.
Improved Uncanny Dodge (Ex): At 5th level and higher, a barbarian can no longer be flanked. This defense denies a rogue the ability to sneak attack the barbarian by flanking her, unless the attacker has at least four more rogue levels than the target has barbarian levels.
Unless the target has 4 more levels in rogue, than a barbarian (for instance) has then the barbarian cannot be flanked at all. Classes that count as rogue, should probably count to the total "rogue" hit dice such as Slayer or Investigator.
Effectively he's immune to flanking. And Outflank nor Seize the Moment can do anything about it.