Arbok
I feel like I should state my argument for Arbok in a different manner, as to better compare it to current threats in the meta:
Arbok's Defensive stats (60/69/79) aren't exactly impressive, but that's exactly what makes it different than any of the other popular Poison-Types in the tier: it's meant to go on the offensive.
Arbok's solid 85 Attack and 80 Speed (the latter being pretty good for NU), accompanied by its faithful boosting move in Coil, as well as amazing coverage moves, makes him a huge threat in the meta. He has two amazing abilities in Intimidate and Shed Skin, giving him at least two viable sets: One being his Offensive Coil set, and another being his Bulky Coil set.
Arbok @ Black Sludge
Trait: Intimidate/Shed Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Coil
- Gunk Shot
- Aqua Tail / Earthquake
- Sucker Punch
This set is more powerful than you would think: the EVs max out Arbok's best stats: his Attack and Speed, while allowing him (I believe?) a Lefties (or in this case, Black Sludge) number. The Jolly Nature is to give him that extra speed; this isn't uncommon on setup sweepers, as they are planning to boost regardless and appreciate the extra speed. Coil is the crux of the set: it's an amazing setup move for Arbok and allows him to tank hits as he boosts his attack and accuracy, creating a very scary Gunk Shot once he reaches +2 or +3 (neither of which are uncommon if played right.) Gunk Shot is an amazing STAB after a few coils, giving it near perfect accuracy. With it's 30% poison chance, it even has the ability to cripple a stubborn wall that you're setting up on, such as Alomomola (who basically does nothing to you if you have Shed Skin.) or Choice-Locked attackers like Primeape, who undoubtedly hates being poisoned. Aqua Tail and Sucker Punch are the preferred coverage moves, allowing Arbok to hit Golurk extremely hard if it decides not to attack, as well as Fire-Types like Charizard, who have a slightly tougher time getting through Arbok without a SE attack (so basically Charizard's Special set doesn't do very well against Arbok without sun up, but he can manage, imo.) Earthquake can be used to no be completely walled by Lairon and other Steel-Types, but they are uncommon and can be covered easily. It can also potentially help you with Scolipede, but that can also be covered by partners. Sucker Punch is an amazing move in this meta as it allows Arbok to OHKO Jynx, an invaluable asset to any team. Overall, this set is really good with hazards up and can benefit from some Screen support, though uncommon, as Arbok then becomes a formidable boosting wall. A downside to this is that Arbok really has no answer to Weezing (though he also walls Scolipede, so no surprises there.), so he's best partnered with a strong Psychic type like Jynx.
Arbok @ Black Sludge
Trait: Shed Skin
EVs: 192 HP / 252 Atk / 64 Spe
Adamant Nature
- Coil
-Rest
- Gunk Shot
- Aqua Tail / Sucker Punch
This set is more focused on boosting until you need to Rest, Rest up, and wake up using Arbok's secondary ability, Shed Skin. The EVs listed are a little odd, but they have a reason: the 64 Speed EVs let Arbok outspeed base 56 mons such as Exeggutor and Torterra, both of which are hit heavily by +1 or +2 Gunk Shot (*I'm pretty sure it has a chance to OHKO Exeggutor with no boosts, but don't quote me. I'm in school and don't have a calc available. Besides, it's irrelevant since you should boost anyways for accuracy purposes.) The rest are dumped into HP and Attack to maximize Arbok's wallbreaking capabilities. Adamant nature goes in hand with the previous statement.
Coil, again, is the crux of the set. Arbok can set up in the face of some of the most formidable walls in the tier, such as Alomomola and Vileplume, all the while boosting it's already decent attack and lackluster Defenses, as well as boosting his accuracy, making his STAB 120 BP Gunk Shot without risks or drawbacks. Rest is an amazing move for this set, as it lets Arbok get completely healthy while keeping his boosts. Shed Skin makes sure this isn't as risky, as Arbok has a 1/3 chance of waking up every turn. As he is already decently hard to take down by +3, it can be rather easy to stay healthy. Gunk Shot is standard, as it lets Arbok hit anything hard with a few boosts. Aqua Tail is the ideal coverage move, letting Arbok hit everything that walls him, basically, for some sort of neutral damage. Sucker Punch can be used if you don't have Paralysis support, but it doesn't hit as much that Aqua Tail does.
In short, Arbok is a great mon who can set up on the tier's Fighting-Types and walls with ease and do serious damage to the opposition. I nominate for him to stay in B-Rank.