Azuril for Mid Tier. It is available early, you get Frustration (and later Return) for an easy STAB and it will evolve fairly early. Once it evolves into Marill, it is one level off from evolving into Azumaril and then it gets Aqua Tail. Using a combination of Aqua Tail/Return/Dig/Filler really gets the job done. And it is easily trainable due to the Desert having a battle with a Breeder and Darumaka/Sandile running around. Only problem is that it is fighting for that Water spot with Oshawatt and once the late game comes, Oshawatt has it outmatched.
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