You can also use a Mareanie/Toxapex as a support wall, especially because it learns Wide Guard, and sweep through with an Ampharos (Moveset : Power Gem, Stab Electric move, Thunderwave)
You can use Mareanies/Toxapex turn to heal the Sweeper you are using, because it tanks most attacks very well.
I was really surprised when i didnt have much issue with shelly when I used that strategy.