when did eridan go grimdark?

Someone mentioned that Hussie described Eridan’s snapping as ‘going Grimdark’ a while ago? He even gets darker in those few panels. However, I don’t know if Hussie canonically did describe this as Grimdarkness, and there’s just no corrupting influence- So I mark that as only ‘aesthetic Grimdarkness’, as in, the story flipped to a more Grimdark tone, rather than “Hey, Eridan is now corrupted”.