I provide evidence that Merc is indeed Zonbei resurrected:

Taken from the wiki: (bolding mine)

“Studies now show that no one here ever liked him. Ever. He would constantly make dumb comments and claim that it was a unique way of trolling everyone. Zonbei would also spend an unnecessary amount of time telling chat that he would be leaving only to reenter minutes after he left.

Few players had encounters with him outside of chat. However, their stories are terrifying: Zonbei was known to Tubmail “females” in-game with awkward flirting and creepy hints at real life meetings.