Wailord @ Mystic Water
Ability: Oblivious
EVs: 252 HP / 252 SpA / 4 SpD
Modest Nature
- Rest
- Rain Dance
- Water Spout
- Sleep Talk
Mystic water boosts the power of water spout, rain dance is for setting up. Use rest when you take some damage. This restores health and also makes wailord immune to other status conditions, such as toxic, which absolutely cripples wailord as it deals large amounts of damage if left alone. However, sleep talk ensures you can continue to attack while asleep.
Mystic water could be swapped for leftovers however, just for a bit of extra healing.
Max hp EVs to add to Wailord's considerable health pool and max EVs on Special attack so water spout can wreck things.
I chose water spout due to the power based off the % of health left of the user, so the bulk on wailord is perfect for this.