I do have Shadow Mag, but I'm at insufficient funds, so I stick with Ferro lead, AS Sha Tentacruel, and PuP Poliwrath. So far it performs well, even better with a Water lead, especially Lanturn.
Think about what cress and walrein weaknesses are and something that could cover that. Maybe typhlosion or Tina if you have one. Or shadow ampharos. Pvpoke might be able to help you find a third as well
That stupid cups, see, double weakness to grass in the back, with a lucario lead, one of the sqishiest poke ever…you could never run that in open, until now, now you can run everything because it’s just depended on rng nowadays, awful what that game has become