>>49207850ZU, maybe PU. Arbok's problems are:
>Low BSTArbok has incredibly low BST for a fully evolved Pokemon, even after its +10 attack buff. For example, all of these Pokemon have a higher BST than Arbok: Doublade, Seaking, Piloswine, Cherrim, Noctowl, Purugly, Sliggoo, Golbat, Swellow, Banette, Dusclops, Jumpluff, Lunatone, Solrock, Greedent, Magneton, Swanna, Dewgong, and Stantler.
To escape the bottom tiers, Arbok would need either: Better defenses (could be accomplished by eviolite + an evolution or some heavy stat boosts to defense and hp), or better speed. Base 80 isn't cutting it. Base 100 would be pretty decent, though, especially with access to Glare, Coil, and Gunk Shot.
>Mediocre move poolIt has decent support moves and a lot of coverage, but it lacks anything that gives it that "oomph" that has saved several Gen 1 Pokemon. Its only STAB being Poison hurts in particular, since even if it does have a high powered attack, it struggles to bust through anything resistant/immune to Poison due to its middling stats. Pokemon with weak stats can often overcome their inherent weaknesses with high powered moves and a strong niche, like Staraptor or Talonflame, but Arbok doesn't have that X factor.
>Mediocre abilitiesAgain, Intimidate and Shed Skin aren't necessarily bad abilities, but they don't provide the extra power needed to push Arbok into relevancy even in NU or RU. Intimidate is a great ability on a Pokemon that can make use of it, but Arbok's best sets don't see it switching a lot, and it doesn't have any switch moves like Parting Shot, U-turn, or Flip Turn. It's basically a shitty off-brand Gyarados, and Gyarados is struggling in UU and has a much higher stat total.
