Greetings, all! I've never relied upon Improved Uncanny Dodge before. According to the Game Guide, Iuz is Cleric20/Rogue10. It's that Rogue10 we're most concerned about here due to how Improved Uncanny Dodge works. Would a Barbarian1/Rogue13 be able to flank Iuz? It was unclear whether a multiclass character needs (Improved) Uncanny Dodge from each class I want to count, or if class levels alone are enough. Improved Uncanny Dodge (Ex) A rogue of 8th level or higher can no longer be flanked. This defense denies another rogue the ability to sneak attack the character by flanking her, unless the attacker has at least four more rogue levels than the target does. If a character already has uncanny dodge from a second class, the character automatically gains improved uncanny dodge instead, and the levels from the classes that grant uncanny dodge stack to determine the minimum rogue level required to flank the character.
It should work presupposing there are no hidden coding preventing that(and I have played games where the programmers broke the rules in that manner)
I would say that would not be enough to beat Iuz's uncanny dodge due to the fact that Barbarians don't get uncanny dodge until 2nd level, the 1 level of Barbarian therefore can't advance the Rogue's uncanny dodge ability to 14 levels worth of ability with this feat.
