The item is slept on. It has the same stats as youmuus but 200G cheaper. Also the passive is worth if they have any shields at all. If the supp gives a tiny 50hp shield from aery, serpents does like 200 extra damage to that target
Yeah I think people get pretty hung up on the passive and ignore the fact that it is one of the highest damage/gold purchases you can buy as a lethality user (post-mythic). If a team has any shields at all and you're an assassin, you should be thinking about this item.