Really, like in the title. From time to time I get really confused when I try to find something that I am sure I've seen some time ago. And nothing. Different tag combo. Nothing. Usually I end looking on different sites that are less respectful to artists to see if I dreamed whole artist. Then I can find name and see that now it's on DNP list.

Good idea? Bad idea? Not possible idea?

Search using status:any or status:deleted to see deleted posts.

You can see takedowns here.

There is already a list. But the takedowns are often anonymous. And I doubt this will change.
https://e621.net/takedowns

You can also use delreason:takedown* to get only results that have been deleted through a takedown. If you know anything else about the image, like say species or gender, it should allow you to quickly find what you're looking for.
When you open the submission page you can also then click the link in the deletion reason to directly view the takedown request itself, or see if there are any sources to check it out at the artist's gallery.

Thank you. I all the time learn new things, forget and relearn mechanics on this site.