Arbok

Type Tier
Poison UU
Statistics
Stat
HP
60
323
Atk
85
268
Def
69
236
Spc
65
228
Spe
80
258
Name Moveset

Wrapper

~ Earthquake
~ Wrap
~ Glare
~ Hyper Beam

Arbok can really only be used well in the underused environment, but should it stray, the likes of Starmie, Alakazam, Golem, Rhydon, Exeggutor and such will eat it for lunch (well, at least Arbok can potentially paralyze the last three before dying). Its defenses are really poor, and even if it is hit by something that isn't super effective, it will bite the dust fairly quickly.

You can start off by using Glare, but ideally you will have already slept and paralyzed parts of your opponent's team already. Arbok, barring critical hits, is going to do about 3% damage each turn with Wrap, so it is going to take a long time to get anything into a low enough HP range to be KOed by Hyper Beam or Earthquake. Since neither move receives STAB, you will never do much more than 30% with Hyper Beam and probably not much more than 40-50% with Earthquake if super effective. Your opponent is also likely to keep switching between Pokémon in an attempt to make you miss, and you will be locked into Wrap until you miss while they do this. Arbok is pretty fast for an underused Pokémon, so if you miss on a Pokémon that is not faster, such as Tangela, you can fairly safely Wrap again. You are going to need to get most things to lower than 30% to kill with Hyper Beam, so if you miss on something faster, you should switch and not risk losing Arbok. You can use Arbok to your advantage to switch in another Pokémon if turn after turn they do not switch out a Pokémon, because they will not be able to attack if your Wrap would have continued. Using this opportunity to switch in a sweeper is a great idea. If they are repeatedly switching between just two Pokémon, you can once again switch to your advantage. Arbok does not have much in the way of STAB, although Poison would only really hurt Bug and Grass types, and most underused Grass-types and some Bug-types are part Poison anyway. Hopefully it will not matter, as Wrap should provide you all the offense you need!

Other Options

Body Slam can provide damage and a chance at paralysis with higher accuracy, if you don't want to use Glare. Mega Drain can hurt Rock and Ground types, although Earthquake does so as well, and Arbok has a low Special stat. Rock Slide is an overall decent move, and Screech can force extra switches. You can use Fissure if OHKOs aren't banned, although enough things still outspeed you in RBY to make this risky. It can learn Acid for STAB, but it's not really worth it.

Opinion

Arbok is not going to single-handedly win you many battles. What it can do is throw your opponent off of his or her game sometimes and, with a little luck, endlessly damage your adversary. While Arbok has decent Attack, its HP and Speed are mediocre, and its Defense and Special are bad. It can't so much function as a physical sweeper as it can as a support (and aggravation) Pokémon.

Counters

If, for some reason, you're using Arbok in OU, Rhydon and Golem are counters if you don't have Mega Drain. Alakazam, Exeggutor, Slowbro, or just about anything that gets a STAB Psychic will put quite a dent into Arbok. Snorlax, Zapdos, Articuno, and Moltres can all counter Arbok regardless of set as well since they all will hit Arbok hard and can take hits from any Arbok set.

Chances are that you are using it solely in UU, where Omastar and Kabutops are good counters, again provided it isn't running Mega Drain. Both of them do not fear its non-STAB Earthquake too much, and fear Wrap even less thanks to their part Rock-type. Electabuzz and Arcanine both are faster than Arbok and they have higher Special stats with high-powered moves to hit Arbok with, but they need to be wary of Earthquake. Aerodactyl does not fear Wrap or Earthquake in the least, so if it is not paralyzed, it will perfectly counter Arbok. Dugtrio is also a fearsome counter, having huge Speed and STAB Earthquake.