Arbok has really grown since Gen 1. So many options now, it's a very versatile Pokemon. This set is slightly different, for the Gen 7 games.
Arbok @ Black Sludge
Nature: Adamant / Jolly
EVs: 252 HP / 128 Def / 128 SpD
Poison Jab- STAB and high chance of poisoning and good power
Stomping Tantrum- Ground type is solid coverage against Steel types and works with the next move
Protect- Good for scouting, stalling while they get hurt by poison or you recover with Black Dludge, and if your Protect fails (double Protect), it doubles Stomping Tantrum's power.
Filler- this could be whatever works for you. Seed Bomb and Crunch are good options to cover its weaknesses. Switcheroo, Coil, Dragon Tail. So many good options. I went with Seed Bomb though.
Pretty straightforward. You want to try to poison your opponent then Protect to get their health down and increase yours. If you think you need a little extra power and can survive one or two hits, go for double Protect then a super charged Stomping Tantrum.
If you run Coil, Poison Jab can be replaced with Gunk Shot because of accuracy boost. Or Swords Dance, you can even use Poison Fang because of the higher chance of badly poisoning.
Let me know what you think. Thanks!