Yes, an old enemy of Yoko's that he believed he killed, or that disappeared after one final fight and he wasn't heard from again--until now. I am flexible, so I can say the former option would take longer for them to figure out, while the latter option would have Yoko come to the conclusion sooner. Yoko does not seem the type to fool easily, so it would come as a huge surprise if the former option is what we roll with. I don't think he'd like being duped very much~

Manipulation of sentient beings ranging from humans to animals is a fine idea to me. Should the ability have some sort of discernible weakness, as in he has to have had contact with them at some point? A power like that needs some details that Yoko would understand if they were enemies in the past, and maybe a new surprise that he wasn't prepared for. I believe Toguro was A-class too, so this guy has to be a considerable threat that even Yoko would advise caution against. 

Botan's case is dependent on how soon the suicides appeared. If it was just one suicide case turned into two within the last couple of weeks and Botan suspects a demon might be behind it, I don't think Kurama would refuse her presence, and would instead offer his aid to solve this case. But if he catches wind from Yoko that this might be the work of a Toguro-level threat, he may gently ask her to step away from this one while he asks for help from someone like Hiei to take this one out--unless Yoko's pride demands he finishes off this one for old times sake, which adds a conflict of will between Shuichi and Yoko both.