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You can also take a Black Cleaver on Ashe, instead of the Last Whisper if they don't have a "really" tank. I think the Frozen Mallet can't be removed, because without you're too fragile, and his slow can be stack with your Frost Shot.
For Mundo, you mustn't do this build like you see it, but like you must take it in your game : if they're AD are strong at the begin, take the Thornmail first, if it's the AP, take the Force of Nature, if they're equals, take the Warmog. And the Raduin's shield is a thing I take if the AD are so feed later, but you can take an other Warmog, a Spirit Visage, may a Maw of Malmortius if you want some dps more, just not take the Quicksilver Sash or Cleans, with your 70% of effects res' you don't need it. No need to take the Frozen Mallet if there is some good crowd controller in your team, like Anivia, but I like it : your ennemy have no escape when you want to kill him ! You also can be little offtank if you take Maw of Malmortius & Hextech Gunblade; why the blade ? It give you lifesteal & spellvamp, with it you never lose hp; tested and allowed ;)