I played a game of URF today and this happend. This full AP Irelia 
became immortal everytime he used her W. I dont know if this is suppost to happen or not. I just wanted to report this so i know that you know it too.
There is a clip i recorded where i tried to use my abilities on her when she used W.
No this is not a bug, this is intended. Irelia w reduces % damage that scales with ap, once she gets past a certain amount of ap (300?350?) with max w she has 100% damage reduction, making her take no damage (unless it's true damage). This is how that skill works under all settings, nothing to do with urf. You don't see it happening often in normal games because ppl don't build ap on her.
