>>32713906Arbok's a poison-type physical attacker. Its options for STAB are limited, its speed isn't great, and it gets fucked over by Ground and Psychic moves easily. Really, the only thing Arbok has going for it is that it looks fucking rad.
>>32713906Mimikyu comes with a built-in substitute, its typing gives it a lot of resistances, and few Pokemon resist what Mimikyu has in its movepool.