>In Canalve City, sail to Iron Island. Go down all the way to where there are 2 staircases to take (one going west and the other east). The eastern one leads to Riley, a blue-clothed guy who follows and helps you battle other Trainers. The western staircase leads to a Pokéball containing Iron Tail. That place is small, so you'll find it easily.
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So if you have already been through Iron Island it should be a breeze to get.
