Yohohoho! Spiders you say? Sounds quite nefarious indeed. Hope you don't mind a little humming on Brook's end as they carry out this scheme... he's not exactly fond of spiders either.

So what's the plan, leaving a bunch of spiders in his bed while he's either sleeping, or not there? Or perhaps something like one really big spider so it's less suspicious, but perhaps a really athletic spider, who makes his bed into a web overnight?

... Or something different, that would work too.