Something that resists Arceus-Poisons weaknesses, which are Ground and Psychic, could be used. I think Skarmory fits that bill perfectly, however, Arceus-Poison doesn't resist Skarms weaknesses, so I Giratina-O could complement the core somewhat since it resists Fire and Electric moves as well.
I'd rather use Tentacruel on a stall team, however, since it gets two great utility moves in Rapid Spin and Toxic Spikes while having much less opportunity cost.
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