The Aroma region is accessible after the completion of all Sigil Halls in the Vesryn region and is reached via the train in Blackfist City. You leave all your Pokémon behind but keep your items & money and you can choose a new starter (Mudkip, Torchic, or Treecko). If you leave two of your Vesryn pokemon in the day-care before unlocking the final upgrade in the aroma region, you can later pick them up there. Note: HMs & HM Items work.