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I think a good core could be Tapu Fini + Heatran. I think these two cover each other's weakness fairly well, besides Tapu Fini being weak to electric unless you run earth power.
Is there any worth in running both Tapu Lele and Tapu Koko on the same team? I think if you have something like mega Manetric, maybe because it's a frail mon, or even something like Xurcitree which is powerful but a bit slow.
I was thinking of a similar water with the following (I don't really have sets but I thought of mons that could work well in rain)
Pelipper -
Pelipper @ Damp Rock
Ability: Drizzle
EVs: 248 HP / 200 SpD / 60 Spe
Calm Nature
- U-turn
- Scald / Knock Off
- Hurricane
- Roost
Rain...