wakadanna
since darkness was already chosen for the Logia I'll skip my thoughts on those but the Zoan has to be a Mythological Zoan right? Something that truly compliments Shadows and Darkness so how about something that can control light since at that point he will have pretty much full blown umbrakinesis which would be pretty awesome. Another would be something that helps him resurrect people, a creature with soul manipulation abilities rather than giving someone Big Moms fruit? or maybe something like an Anubis fruit? Maybe that's too 'godly' I know there is a Buddha fruit but is it the same? Might be too much but them already having someone with the Jackal fruit in a desert country is what made it come to mind after thinking of the Zoan fruits that we've already seen. I don't know, there are so many i would choose an ability you want him to have and then search for mythological creatures you can use to give it to him (which is why Mythological Zoans are awesome and will always be better than ancient Zoans). Thankfully it's One Piece so you can stretch it a bit if needed to fit what you want, I mean seriously the Paw Paw fruit should not be able to do what it can do.