A DRI-YWET showed up in my mailbox today. As much as I liked the tarnish, I had to give her a bit of a scrub. 
This thread seams like the appropriate place for this- I received an obsidian 54 in a trade, and want to tarnish it back to its original color. How would I do that?
You mean it’s all cleaned up? If so, time will work its magic.
I’ve heard that some people have had success soaking it in Diet Coke.
Not all cleaned up, but the rims are lighter then I’d like. I was thinking mustard?
That would work since vinegar is in mustard.
Vinegar would also work 
WOAH!! Nice, man! How’d you manage to score that?
What would be the safest? diet coke, mustard, or vinegar? What would be the the most effective?
Is there a way to remove tarnish from a plated yoyo without the needing of a special remover. Like any household items I could use or do I have to go buy tarnish remover?
Polish. I’ve used mothers polish.
If you don’t have any, I’ll bring some to the next meet for you.
do that!